Process for catalytic hydrogenation of halonitroaromatics

ABSTRACT

The present invention generally relates to processes for the catalytic hydrogenation of halonitroaromatics. In particular, the present invention includes processes for the catalytic hydrogenation of halonitroaromatics such as 2,5-dicloronitrobenzene to 2,5-dichloroaniline over a platinum-containing catalyst. The present invention also relates to processes for producing 3, 6-dichloro-2-methoxybenzoic acid.

FIELD OF THE INVENTION

The present invention generally relates to processes for the catalytichydrogenation of halonitroaromatics. In particular, the presentinvention includes processes for the catalytic hydrogenation ofhalonitroaromatics such as 2,5-dicloronitrobenzene to2,5-dichloroaniline over a platinum-containing catalyst. The presentinvention also relates to processes for producing3,6-dichloro-2-methoxybenzoic acid (dicamba).

BACKGROUND OF THE INVENTION

Halonitroaromatic compounds include various mono- and di-halosubstituted nitroaromatics. Specific examples includechloronitroaromatic compounds such as 2-, 3-, and 4-chloronitrobenzene;2,4-dicloronitrobenzene; 2,5-dicloronitrobenzene;3,4-dichloronitrobenzene, among others. The catalytic hydrogenation ofhalonitroaromatics is a reaction of significant industrial importancebecause the resulting haloaminoaromatic compounds (e.g., haloanilines)are useful as intermediates in the production of certain agrochemicals,pharmaceuticals, and polymers. For example, 2,5-dichloroaniline can beused as an intermediate in the production of3,6-dichloro-2-methoxybenzoic acid (also known by its common namedicamba), which is a highly effective and commercially importantherbicide that is useful for controlling a wide variety of unwantedvegetation, including agricultural weeds. Convenient and economicalmethods of preparing dicamba, therefore, are of significant commercialimportance.

Various processes for the catalytic hydrogenation of halonitroaromaticsare described in references such as U.S. Pat. Nos. 3,073,865; 3,145,231;3,291,832; 4,020,107; 4,760,187; as well as Kosak, “Hydrogenation ofHaloaromatic Nitro Compounds,” Catalysis in Organic Synthesis, AcademicPress, London, 1980, 107-117. One problem typically encountered duringthe hydrogenation process is the loss of selectivity to the desiredhaloaminoaromatic product through dehalogenation of thehaloaminoaromatic product. Attempts to solve this problem have focusedon introducing catalyst modifiers or additives into the reaction mediumto suppress the dehalogenation reaction. For example, U.S. Pat. No.3,073,865 describes the addition of a hydroxide or oxide of magnesium tothe reaction medium as a dehalogenation suppressor. U.S. Pat. No.3,145,231 discloses the use of cycloaliphatic amines such piperazine andmorpholine as dehalogenation suppressors. U.S. Pat. No. 4,020,107introduces an acidic phosphorous compound to suppress the dehalogenationreaction. U.S. Pat. No. 4,760,187 uses a ruthenium-platinum catalyst forhalogenating chloronitrobenzenes to chloroanilines that also reducesdehalogenation. Also, Kosak teaches that the use of a sulfided platinumcatalyst is one of the more effective procedures for minimizingdehalogenation.

Although these processes may be effective strategies for minimizingdehalogenation of the halonitroaromatic compound, these processesintroduce additional components to the reaction medium or catalystmaterial. In multi-step processes that include the step of hydrogenatinga halonitroaromatic, introducing additional components to the reactionmixture can affect downstream processes and reactions and maynecessitate further separation operations, which increase process costs.Also, introducing catalyst modifiers can increase process costs andresult in the presence of undesired metal contaminants or the productionof other undesired reaction products.

Accordingly, there remains a need for processes for the catalytichydrogenation of halonitroaromatic compounds that minimize theintroduction of extraneous additives and catalyst modifiers but stillprovide for high selectivity to the haloaminoaromatic product and limitselectivity loss through dehalogenation.

SUMMARY OF THE INVENTION

The present invention is generally directed to processes for thecatalytic hydrogenation of halonitroaromatics to haloaminoaromatics. Forexample, the present invention includes processes for the catalytichydrogenation of halonitroaromatics such as 2,5-dicloronitrobenzene to2,5-dichloroaniline in the presence of a platinum-containing catalyst.The present invention also includes processes for producing3,6-dichloro-2-methoxybenzoic acid (dicamba) using 2,5-dichloroanilineproduced in accordance with the present invention.

Aspects of the present invention are directed to processes for thehydrogenation of halonitroaromatic compounds using catalysts that haveimproved selectivity for the production of haloaminoaromatics. Inparticular, various processes of the present invention provide for areduction in the loss of selectivity to dechlorination (i.e., suppressdehalogenation). Processes in accordance with the present invention withimproved selectivity for haloaminoaromatics significantly improveprocess economics.

Further aspects of the present invention are directed to processes thatminimize or eliminate the addition of extraneous additives to thehydrogenation reaction medium and catalyst while maintaining a highselectivity for the haloaminoaromatic product. Advantageously,minimizing or eliminating extraneous additives reduces or avoids theneed for subsequent processes, such as additional separation processes,to manage these additives, which improves process economics.

Other aspects of the present invention are directed to processes ofusing catalysts which are more stable under various conditions of thehydrogenation reaction (e.g., more resistant to leaching in an acidicsolvent). For example, reduced leaching of platinum from the catalystincreases its useful life and reduces process costs associated withplatinum loss and recovery of platinum from the reaction product.

Still further aspects of the present invention are directed to processesfor preparing 3,6-dichloro-2-methoxybenzoic acid using2,5-dichloroaniline obtained from the hydrogenation processes describedherein as an intermediate.

In various embodiments, the present invention is directed to a processfor preparing a haloaminoaromatic compound comprising: feeding hydrogenand a feed mixture comprising a halonitroaromatic compound to ahydrogenation zone; and reacting the halonitroaromatic compound withhydrogen in the presence of a hydrogenation catalyst comprising platinumon a carbon support to produce a reaction product comprising thehaloaminoaromatic compound, wherein the process further comprises one ormore of the following features:

(1) the hydrogenation catalyst is a calcined hydrogenation catalyst;

(2) the feed mixture further comprises a solvent comprising an acid;

(3) the hydrogenation catalyst is an unmodified hydrogenation catalyst;

(4) the feed mixture is free of dehalogenation suppressors;

(5) the reaction product further comprises 2-chloroaniline and3-chloroaniline and the mole ratio of 3-chloroaniline to 2-chloroanilineis no greater than about 6:1, no greater than about 5:1, no greater thanabout 4:1, no greater than about 3:1, no greater than about 2:1, or nogreater than about 1:1;

(6) the reaction product further comprises 2-chloroaniline and3-chloroaniline, and the loss of selectivity from 2,5-dichloroaniline to2-chloroaniline and 3-chloroaniline is less than about 0.4 mol. %, lessthan about 0.3 mol. %, or less than about 0.2 mol. %; and/or

(7) the hydrogenation catalyst comprises platinum metal particles of asize up to 10 nm in their largest dimension and no more than about 50%(number basis), no more than about 25% (number basis), no more thanabout 20% (number basis), no more than about 15% (number basis), or nomore than about 10% (number basis) of the platinum metal particles areless than 2 nm in their largest dimension.

In further embodiments, the present invention is directed to a processfor producing 2,5-dichloroaniline comprising: feeding hydrogen and afeed mixture comprising 2,5-dichloronitrobenzene and a solventcomprising an acid to a hydrogenation zone; and reacting the2,5-dichloronitrobenzene with hydrogen in the presence of aheterogeneous hydrogenation catalyst comprising platinum on a carbonsupport to produce a reaction product comprising 2,5-dichloroaniline.

Other embodiments of the present invention include a process forproducing 2,5-dichloroaniline comprising: feeding hydrogen and a feedmixture comprising 2,5-dichloronitrobenzene to a hydrogenation zone; andreacting the 2,5-dichloronitrobenzene with hydrogen in the presence of aheterogeneous hydrogenation catalyst comprising platinum on a carbonsupport to produce a reaction product comprising 2,5-dichloroaniline,wherein the hydrogenation catalyst is an unmodified hydrogenationcatalyst and the feed mixture is free of dehalogenation suppressors.

Still further embodiments of the present invention include a process forproducing 2,5-dichloroaniline comprising: feeding hydrogen and a feedmixture comprising 2,5-dichloronitrobenzene to a hydrogenation zone; andreacting the 2,5-dichloronitrobenzene with hydrogen in the presence of aheterogeneous hydrogenation catalyst comprising platinum on a carbonsupport to produce a reaction product comprising 2,5-dichloroaniline,wherein the hydrogenation catalyst is a calcined hydrogenation catalyst.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a series of scanning transmission electron microscopy(STEM) images of the surface of a commercial platinum on carbon catalystprior to calcination.

FIG. 2 presents a series of STEM images of the surface of a commercialplatinum on carbon catalyst after calcination.

FIG. 3 presents a series of STEM images of the surface of a commercialplatinum on carbon catalyst after calcination.

FIG. 4 presents a series of STEM images of the surface of a commercialplatinum on carbon catalyst after calcination and after 15 reactioncycles.

FIG. 5 presents a series of STEM images of the surface of a commercialplatinum on carbon catalyst after calcination and after 15 reactioncycles.

FIG. 6 presents a series of STEM images of the surface of a preparedplatinum on carbon catalyst after calcination.

FIG. 7 presents a series of STEM images of the surface of a preparedplatinum on carbon catalyst after calcination.

FIG. 8 presents a series of STEM images of the surface of a preparedplatinum on carbon catalyst after calcination and after use in 43hydrogenation reaction cycles.

FIG. 9 presents a series of STEM images of the surface of a preparedplatinum on carbon catalyst after calcination and after use in 43hydrogenation reaction cycles.

FIG. 10 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst before calcination.

FIG. 11 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst before calcination.

FIG. 12 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst after calcination.

FIG. 13 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst after calcination.

FIG. 14 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst after calcination in the presenceof 5% hydrogen gas.

FIG. 15 presents a series of STEM images of the surface of an un-reducedplantinum precursor on carbon catalyst after calcination in the presenceof 5% hydrogen gas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various processes in accordance with the present invention for theproduction of a haloaminoaromatic compound generally includecatalytically reducing a halonitroaromatic compound with hydrogen in thepresence a hydrogenation catalyst. In particular, processes inaccordance with various aspects of the present invention comprisefeeding hydrogen and a feed mixture comprising a halonitroaromaticcompound to a hydrogenation zone and reacting the halonitroaromaticcompound with hydrogen in the presence of a hydrogenation catalyst toproduce a reaction product comprising a haloaminoaromatic compound.Generally, the hydrogenation catalyst is heterogeneous and comprisesnoble metal (e.g., platinum) particles on a carbon support. Noble metalsinclude platinum, palladium, ruthenium, rhodium, iridium, silver,osmium, and gold. Platinum is a preferred noble metal. The reactionscheme for the hydrogenation of a halonitrobenzene compound withhydrogen gas to a haloaniline is as follows:

where X is one or more halo substituents (e.g., 1, 2, or 3) such asfluoro, chloro, bromo, or iodo.

The processes of the present invention can be used for the conversion ofvarious halonitroaromatic compounds. For example, the halonitroaromaticcompound can be a halonitrobenzene compound (e.g., 2-, 3-,4-chloronitrobenzene). The halonitroaromatic compounds can have one,two, or more halo substituents. In various embodiments, thehalonitroaromatic compounds comprise dihalo-substituted nitrobenzenes,such as dichloronitrobenzenes. Specific examples ofdichloronitrobenzenes include 2,4-dicloronitrobenzene;2,5-dicloronitrobenzene; 3,4-dichloronitrobenzene; and3,5-dichloronitrobenzene.

One preferred halonitroaromatic compound comprises2,5-dicloronitrobenzene, which is a useful intermediate in theproduction of 3,6-dichloro-2-methoxybenzoic acid (dicamba). Accordingly,various processes of the present invention are directed to hydrogenationof 2,5-dichloronitrobenzene to 2,5-dichloroaniline, which is shown inthe reaction scheme below. The processes generally comprise feedinghydrogen and a feed mixture comprising 2,5-dichloronitrobenzene to ahydrogenation zone; and reacting the 2,5-dichloronitrobenzene withhydrogen in the presence of a heterogeneous hydrogenation catalystcomprising platinum on a carbon support to produce a reaction productcomprising 2,5-dichloroaniline.

The halogenation reaction is nearly quantitative in that the yield of2,5-dichloroaniline is at least about 90%, at least about 92%, at leastabout 95%, at least about 98%, or at least about 99%. However, as noted,the 2,5-dichloroaniline product can be further reduced resulting indehalogenated compounds such as 2- and 3-chloroaniline. Thedehalogenation reaction can proceed as follows:

The dehalogenation reaction results in a loss of selectivity to the2,5-dichloroaniline product.

Applicants have discovered that the loss of selectivity resulting fromthe dehalogenation of the haloaminoaromatic product (e.g.,2,5-dichloroaniline) can be reduced by controlling or adjusting theplatinum particle size distribution on the hydrogenation catalyst.Without being bound by theory, applicants believe that thedehalogenation reaction is dependent at least in part on the platinumparticle sizes on the carbon support of the catalyst. The presence ofvery small platinum particles (e.g., <2 nm and sub-nm in diameter)and/or any unreduced Pt(II) species on the carbon support in theas-synthesized catalyst are thought to be structurally more favorable tothe dehalogenation reaction. Providing a catalyst having a smallerproportion of these particles has been found to reduce the loss ofselectivity to the haloaminoaromatic product resulting fromdehalogenation. Larger platinum particles on the carbon support surfacehave been found to be more stable under reaction conditions andstructurally less favorable to dechlorination mechanism. Accordingly,the processes of the present invention provide for a reduction in theloss of selectivity to dechlorination. For example, for thehydrogenation of 2,5-dichloronitrobenzene to 2,5-dichloroaniline, theloss of selectivity from 2,5-dichloroaniline to 2-chloroaniline and3-chloroaniline can be less than about 0.4 mol. %, less than about 0.3mol. %, or less than about 0.2 mol. %.

In accordance with various embodiments of the present invention, thehydrogenation catalyst exhibits a reduced population of smaller platinummetal particles or crystallites (e.g., metal particles having a particlesize in their largest dimension of less than about 2 nm). These lessdesirable smaller metal particles are also more susceptible to leachingthan larger particles, particularly when the catalyst is used in anacidic environment that has the potential to solubilize platinum metals.Catalysts exhibiting a platinum particle size distribution in which theproportion of smaller metal particles or crystallites is reduced may beobtained using the strategies described herein.

As noted, the hydrogenation reaction can result in the formation ofundesired dehalogenation compounds. However, some of thesedehalogenation compounds may be more easily separated from certainreaction products than others. For example, processes for producing3,6-dichloro-2-methoxybenzoic acid (dicamba) include the step ofreducing 2,5-dichloronitrobenzene to 2,5-dichloroaniline, as describedherein. The hydrogenation reaction product can comprise dehalogenationcompounds such as 2-chloroaniline and 3-chloroaniline. In a subsequentstep of the dicamba production process, 2,5-dichloroaniline is convertedto 2,5-dichlorophenol. During this conversion, 2- and 3-chloroanilineare converted 2- and 3-monochlorophenol, respectively. 3-Chlorophenol isdifficult to separate from 2,5-dichlorophenol via distillation becauseof its close boiling point to 2,5-dichlorophenol (214° C. vs. 211° C.).On the other hand, 2-monochlorophenol has a much lower boiling point(175° C.) than 2,5-dichlorophenol, which provides for a more effectiveseparation via distillation. Thus, in this case, assuming dehalogenationcannot be entirely eliminated, then 2-chloroaniline is a preferreddehalogenation compound over 3-chloroaniline.

It has been further discovered that dechlorination selectivity (e.g.,selectivity to 2-chloroaniline over 3-chloroaniline) is also dependenton platinum particle size of the platinum catalyst. Without being boundby theory, this structure sensitivity of dechlorination is likely due tothe platinum particle size effect where smaller platinum particles havea more open structure providing less steric hindrance to the bulkyortho-Cl atom that is positioned next to the amine group that binds ontothe platinum site. As such, this particle structure is thought to leadto the formation of 3-chloroaniline. In the case of larger platinumparticles, the steric effect from the neighboring platinum atoms on theortho-Cl atom is thought to lower the pre-exponential factor of theArrhenius equation (collision frequency), thus lowering the rate offormation of 3-chloroaniline. Accordingly, various processes of thepresent invention for hydrogenating 2,5-dichloronitrobenzene to2,5-dichloroaniline provide for a reduced mole ratio of 3-chloroanilineto 2-chloroaniline in the reaction product. In various embodiments, themole ratio of 3-chloroaniline to 2-chloroaniline in the reaction productis no greater than about 6:1, no greater than about 5:1, no greater thanabout 4:1, no greater than about 3:1, no greater than about 2:1, or nogreater than about 1:1. For example, the mole ratio of 3-chloroanilineto 2-chloroaniline can range from about 0.5:1 to about 6:1, from about0.5:1 to about 5:1, from about 0.5:1 to about 4:1, from about 0.5:1 toabout 3:1, from about 0.5:1 to about 2:1, from about 1:1 to about 6:1,from about 1:1 to about 5:1, from about 1:1 to about 4:1, from about 1:1to about 3:1, or from about 1:1 to about 2:1.

Hydrogenation Catalyst

Methods used to deposit the platinum onto the surface of the carbonsupport are generally known in the art, and include liquid phase methodssuch as reaction deposition techniques (e.g., deposition via reductionof platinum metal compounds, and deposition via hydrolysis of platinummetal compounds), ion exchange techniques, excess solution impregnation,and incipient wetness impregnation; vapor phase methods such as physicaldeposition and chemical deposition; precipitation; electrochemicaldeposition; and electroless deposition. Deposition of platinum onto thecarbon support may comprise, for example, reductive deposition wherein asurface of a carbon support is contacted with a solution comprisingreducing agent and a compound comprising the platinum. Reducing agents,include for example, formaldehyde, formic acid, hydrazine, citric acid,polyols (e.g., ethylene glycol), and sodium borohydride.

As noted, the hydrogenation catalysts used in the processes of thepresent invention comprise noble metal (e.g., platinum) particles on thesurface of a carbon support. The presence of very small platinumparticles and/or any unreduced Pt(II) species on the carbon support inthe catalyst are thought to be structurally more favorable to thedehalogenation reaction. Providing a catalyst having a smallerproportion of these particles has been found to reduce the loss ofselectivity to the haloaminoaromatic product resulting fromdehalogenation. In accordance with the present invention, one strategyfor providing a catalyst having a reduced proportion of platinumparticles of less than 2 nm and a smaller proportion of unreduced Pt(II)species is to subject the catalyst to a calcination treatment.Subjecting the catalyst to a calcination treatment generally affects theparticle size distribution of platinum metal particles present on thesurface of the carbon support. In particular, high temperatures of thecalcination induces controlled agglomeration of small platinum particleson the carbon surface thereby forming larger platinum particles, whichare more stable and structurally less favorable to the dechlorinationreaction. Also, calcination reduces the proportion of unreduced Pt(II)species such that the hydrogenation catalyst has a Pt(II) content thatis less than about 0.1 wt. %, less than about 0.05 wt. %, or less thanabout 0.01 wt. % of the total weight of platinum. Accordingly, processesof the present invention include use of a calcined hydrogenationcatalyst.

Temperatures below 500° C. are generally unsatisfactory for calcination.On the other hand, subjecting the catalyst to temperatures in excess of1200° C. promotes graphitization of the carbon support and/orover-sintering of the metal particles. Graphitization of the carbonsupport and over-sintering of the metal particles tends to reduce theactivity of the catalyst by reducing the surface areas of catalyticallyactive carbon and platinum metal. In addition, such a reduction inexposed surface area of catalytically active platinum metal is anuneconomical use of costly platinum metal. Thus, generally, the catalystis heated to a temperature of at least about 500° C., for example fromabout 500° C. to about 1200° C.

To attain a catalyst exhibiting the desired particle size distribution,the surface of the catalyst is typically heated to a temperature of atleast about 600° C., at least about 700° C., at least about 800° C., orat least about 900° C. For example, the catalyst can be subjected to aheat treatment temperature of from about 500° C. to about 1000° C., fromabout 600° C. to about 1000° C., from about 700° C. to about 1000° C.,from about 800° C. to about 1000° C., from about 500° C. to about 950°C., from about 600° C. to about 950° C., from about 700° C. to about950° C., or from about 800° C. to about 950° C. In particular, heatingthe surface of the carbon support to a temperature at least as high asthese minimums and within these ranges, has an advantageous effect inpromoting the formation of platinum metal particles on the surface ofthe carbon support having a particle size distribution in which thepopulation of smaller metal particles (e.g., those particles less thanabout 2 nm or less in their largest dimension) is reduced. Calcinationalso enhances the stability of the catalyst because larger platinumparticles on the carbon support are more resistant to leaching thansmaller particles.

Typically, the catalyst is calcined in an inert, non-oxidizingenvironment. The inert, non-oxidizing environment may consistessentially of inert gases such as nitrogen, noble gases (e.g., argon,helium) or mixtures thereof.

It is optionally for hydrogen to be present in the non-oxidizingenvironment of the calcination process due to the small molecular sizeof the hydrogen that allows better penetration into the deepest pores ofthe carbon support. The concentration of hydrogen may vary, althoughhydrogen contents of no more than about 5% by volume are preferred.Typically, hydrogen can be present in the calcination atmosphere at aconcentration of from about 1 to about 5% by volume and, more typically,from about 2 to about 5% by volume. The remainder of the gas may consistessentially of a non-oxidizing gas such as nitrogen, argon, or helium.Such non-oxidizing gases may be present in the calcination atmosphere ata concentration of at least about 90% by volume, from about 90 to about99% by volume, and from about 95 to about 98% by volume.

Calcination following metal deposition can comprise high-temperaturegas-phase reduction to remove oxygen-containing functional groups fromthe surface of the catalyst, thereby attaining a catalyst exhibiting thecarbon monoxide desorption and/or carbon atom to oxygen atom surfaceratio characteristics as described in U.S. Pat. No. 6,417,133.

As the number of smaller platinum particles is reduced, the surface areaof exposed metal on the carbon support also decreases. The total exposedmetal surface area of catalysts of the present invention may bedetermined using static carbon monoxide chemisorption analysis.

Exposed metal surface area (m² per gram catalyst) may be determined fromthe volume of CO chemisorbed using the following equation:

Metal surface area (m²/g catalyst)=6.023*10²³*V/2*SF*A/22,414, where:

-   -   V=volume of CO chemisorbed (cm³/g STP) (Volume of one mole of        gas is 22,414 cm³    -   STP, i.e., the volume of one μmole of CO is 0.022414 cm³)    -   SF=stoichiometry factor (assumed to be equal to 1, i.e., one CO        molecule per exposed Pt atom)    -   A=effective area of one exposed Pt atom (m²/atom) (8×10⁻²⁰        m²/atom of Pt)

A further strategy for providing a catalyst having a reduced proportionof platinum particles of less than 2 nm involves calcining an unreducedplatinum catalyst precursor. In this strategy, unreduced platinum isdeposited on a carbon support to form the catalyst precursor (i.e.,deposited without use of a reducing agent). Subsequently, the catalystprecursor is calcined as described herein. Calcination at thetemperatures stated herein reduces the platinum metal and results inmore platinum agglomeration, which can lower the proportion of smallplatinum particles on the catalyst.

Other techniques to modify the platinum particle size distribution ofthe hydrogenation catalyst include procedures for the controlledhydrolysis and deposition of platinum precursors onto activated carbonto achieve larger platinum clusters (e.g., using polyols, strongerreducing agents, pre-formed colloidal Pt or Pt-ligand complexes).

Another strategy for providing a catalyst having a reduced proportion ofplatinum particles of less than 2 nm involves modifying the carbonsupport prior to platinum deposition by selectively blocking relativelysmall pores (e.g., micropores). Pore blocking preferentially preventsdeposition of platinum within pores that would be inaccessible to one ormore reactants. Pore blockers used to selectively block micropores maybe selected from a variety of compounds including, for example, varioussugars (e.g., sucrose), 5- or 6-member ring-containing compounds (e.g.,1,3- and 1,4-disubstituted cyclohexanes), and combinations thereof.Compounds suitable for use in connection with selective blocking ofmicropores include 1,4-cyclohexanedimethanol (1,4-CHDM),1,4-cyclohexanedione bis(ethylene ketal), 1,3- or1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexane dione monoethyleneacetal, and combinations thereof.

The pore blockers may comprise the product of a reaction (e.g., acondensation reaction) between one or more pore blocking compoundprecursors. Once formed, the resulting pore blocking compound may bepreferentially retained within selected pores of the support by virtueof having at least one dimension that prevents the pore blockingcompound from exiting the pores.

For example, it has been observed that the coupling product of acyclohexane derivative and a glycol may be utilized as a micropore poreblocking agent for particulate carbon supports used to support aplatinum metal or other metal catalyst. More particularly, the poreblocking agent may be the coupling product of a di-substituted,tri-substituted, or tetra-substituted cyclohexane derivative and aglycol. In particular, the cyclohexane derivative may be selected fromthe group consisting of 1,4-cyclohexanedione, 1,3-cyclohexanedione,1,4-cyclohexanebis(methylamine), and combinations thereof. The glycol isgenerally selected from the group consisting of ethylene glycol,propylene glycol, and combinations thereof.

Generally, the support is contacted with a liquid comprising the poreblocking agent or one or more precursor(s) of the pore blocking agent.Typically, the support to be treated is contacted with a mixture orsolution comprising one or more pore blocking compounds or precursor(s)dispersed or dissolved in a liquid contacting medium (e.g., deionizedwater). For example, the support may be contacted with a mixture orsolution including a cyclohexane derivative and a glycol, or a liquidcontacting medium consisting essentially of the cyclohexane derivativeand glycol. The support may also be sequentially contacted with liquidsor liquid media comprising one or more of the precursors.

Regardless of whether a compound that ultimately functions as a poreblocker is introduced into pores of the support or precursors that formthe blocking compound are introduced into the support, pore blockers maybe preferentially retained within selected support pores (e.g.,micropores) by virtue of the conformational arrangement assumed by thepore blocking agent once disposed or formed within the pores. Forexample, it is currently believed that various pore blocker moleculestransform from a more linear chair conformation to a bulkier boatconformation, which conduces trapping of the compound within themicropores. In particular, it is currently believed that various poreblocking agents including a hydrophilic end group will favor a boatconformation within the micropore(s) of a porous carbon support becauseof the nature of the carbon support (i.e., the boat conformation will befavored by a pore blocking compound having hydrophilic end groupsbecause of the relatively hydrophobic nature of the carbon supportsurface). Examples of pore blocking compounds including a hydrophilicend group include 1,4-cyclohexanedicarboxylic acid and1,4-cyclohexanedimethanol (CHDM).

A conformational change of a pore blocker also may be promoted orinduced by manipulating the liquid medium comprising the pore blockingagent in contact with the support including, for example, adjusting thepH and/or adjusting the temperature of the liquid medium.

As noted, it is believed that contacting the support with the poreblocking agent or precursors results in pore blocking agent beingintroduced into or disposed within support micropores, and within largerpores outside this predefined range. In order to provide a treatedsupport in which the micropores within the predefined range arepreferentially blocked, the support is subsequently contacted with awashing liquid to remove the blocking agent from pores outside themicropore domain (i.e., those pores in which the pore blocking agentwill not be preferentially retained by virtue of the agent having atleast one dimension larger than the pore opening).

Employing one or more of these strategies provides a catalyst having areduced proportion of platinum particles that are less than 2 nm. Invarious embodiments, the platinum particles of the catalyst arecharacterized as having a particle size distribution (as determinedusing electron microscopy) such that with respect to platinum metalparticles of a size up to 10 nm in their largest dimension, no more thanabout 50% (number basis), no more than about 25% (number basis), no morethan about 20% (number basis), no more than about 15% (number basis), orno more than about 10% (number basis) of the platinum metal particlesare less than 2 nm in their largest dimension. Also, at least about 25%(number basis, at least about 40% (number basis), at least about 50%(number basis) or at least about 60% (number basis), at least about 70%(number basis), or at least about 80% (number basis) of the platinummetal particles up to 10 nm in their largest dimension are from 2 nm to10 nm in their largest dimension.

Generally, the platinum metal particles up to 10 nm in their largestdimension can be characterized as having average particle size ofgreater than about 2.5 nm, greater than about 3 nm, greater than about 4nm, or greater than about 5 nm. The average particle size of theplatinum metal particles up to 10 nm in their largest dimension canrange from about 2.5 to about 8 nm, from about 3 to about 7 nm, fromabout 3 to about 6 nm, or from about 3 to about 4 nm.

The particle size distribution of platinum metal particles at thesurface of the carbon support may be determined using various techniquesknown in the art, including electron microscopy. The particle sizedistribution is characterized with respect to particles of a size lessthan 10 nm in their largest dimension. However, it should be recognizedthat the catalyst of the present invention may contain larger particles(e.g., from 10 to 15 nm or even larger).

The hydrogenation catalyst typically has a platinum loading that is nogreater than about 5 wt. % of the total catalyst weight. Although higherplatinum loadings may provide for a greater amount of catalytic sites,it has been found that lower platinum loadings are suited for thehydrogenation reaction, which beneficially reduces catalyst costs.Accordingly, the hydrogenation catalyst can have a platinum loading thatis no greater than about 4 wt. %, no greater than about 3 wt. %, nogreater than about 2 wt. %, no greater than about 1.5 wt. %, or nogreater than about 1 wt. % of the total catalyst weight. For example,the hydrogenation catalyst can have a platinum loading that is fromabout 0.1 wt. % to about 5 wt. %, from about 0.1 wt. % to about 4 wt. %,from about 0.1 wt. % to about 3 wt. %, from about 0.1 wt. % to about 2wt. %, from about 0.1 wt. % to about 1.5 wt. %, from about 0.1 wt. % toabout 1 wt. %, from about 0.5 wt. % to about 5 wt. %, from about 0.5 wt.% to about 4 wt. %, from about 0.5 wt. % to about 3 wt. %, from about0.5 wt. % to about 2 wt. %, from about 0.5 wt. % to about 1.5 wt. %, orfrom about 0.5 wt. % to about 1 wt. % of the total catalyst weight.

As noted, the hydrogenation catalyst comprises platinum on a carbonsupport. Preferably, the carbon support of the hydrogenation catalystcomprises activated carbon. Activated, non-graphitized carbon supportsare preferred. These supports are characterized by high adsorptivecapacity for gases, vapors, and colloidal solids and relatively highspecific surface areas. The support suitably may be a carbon, char, orcharcoal produced by means known in the art, for example, by destructivedistillation of wood, peat, lignite, coal, nut shells, bones, vegetable,or other natural or synthetic carbonaceous matter, but preferably is“activated” to develop adsorptive power. Activation usually is achievedby heating to high temperatures (e.g., >800° C.) with steam or withcarbon dioxide which brings about a porous particle structure andincreased specific surface area.

The carbon support of the hydrogenation catalyst generally possesses arelatively large surface area. The total specific surface area of thecarbon support, as measured by the Langmuir method using N₂, istypically at least about 500 m²/g, at least about 600 m²/g, at leastabout 800 m²/g, more preferably at least about 900 m²/g, at least about1000 m²/g, at least about 1100 m²/g, or at least about 1200 m²/g. Forexample, the total specific surface area of the carbon support, asmeasured by the Langmuir method using N₂ can be from about 500 m²/g toabout 3000 m²/g, from about 750 m²/g to about 3000 m²/g, from about 1000m²/g to about 3000 m²/g, from about 1250 m²/g to about 3000 m²/g, orfrom about 1500 m²/g to about 3000 m²/g. In certain embodiments, thetotal surface area of the support is from about 1500 m²/g to about 2000m²/g or from about 2500 m²/g to about 3000 m²/g. It is understood thatthese values generally correspond to those measured by the likewisewell-known Brunauer-Emmett-Teller (B.E.T.) method using N₂.

The Langmuir surface area of the carbon support attributable to poreshaving a diameter of less than 2 nm (i.e., micropores) is typically atleast about 750 m²/g, at least 1000 m²/g, or at least about 1250 m²/g.The Langmuir micropore surface area of the carbon support can be fromabout 750 m²/g to about 2000 m²/g, from about 1000 m²/g to about 2000m²/g, or from about 1250 m²/g to about 2000 m²/g. The Langmuir surfacearea of the carbon support attributable to pores having a diameter ofgreater than 2 nm (i.e., mesopores and macropores) can be from about 100m²/g to about 1000 m²/g, from about 200 m²/g to about 800 m²/g, or fromabout 300 m²/g to about 800 m²/g.

As indicated, a relatively large portion of the surface area of thecarbon support can be attributable to micropores. In variousembodiments, at least about 50%, at least about 60%, at least about 70%,or at least about 80% of the total Langmuir surface area of the carbonsupport is attributable to micropores. In these and other embodiments,from about 50% to about 90%, from about 60% to about 90%, or from about65% to about 85% of the total Langmuir surface area of the carbonsupport is attributable to micropores.

The carbon support can also have an average pore diameter that is in therange of from about 0.5 nm to about 5 nm, from about 1 nm to about 5 nm,from 1 nm to about 4 nm, from about 1 nm to about 3 nm, or from about 2nm to about 5 nm. Further in accordance with the present invention, thecarbon support can have a pore volume of at least about 0.3 ml/g, atleast about 0.4 ml/g, or at least about 0.5 ml/g. The carbon support canhave a pore volume of from about 0.1 to about 2.5 ml/g, from about 0.2to about 2.0 ml/g, or from about 0.4 to about 1.5 ml/g. Also, the carbonsupport can have a pore volume that is from about 0.3 ml/g to about 0.1ml/g, or from about 0.5 ml/g to about 0.1 ml/g that is attributable topores of a diameter from 0.5 nm to 5 nm.

The support can be a monolithic support. Suitable monolithic supportsmay have a wide variety of shapes. Such a support may be, for example,in the form of a screen or honeycomb. In various embodiments, thesupports are in the form of particulates. Suitable particulate supportsmay have a wide variety of shapes. For example, such supports may be inthe form of granules. The support can also be in the form of a powder orparticulate. These particulate supports may be used in a reactor systemas free particles, or may be bound to a structure in the reactor system,such as a screen or an impeller.

One approach commonly used to suppress the dehalogenation of thehaloaminoaromatic product is through the incorporation of a catalystmodifier in the form of a metal promoter (e.g., copper, nickel,ruthenium; either as alloy or co-metal, on the platinum on carboncatalyst) or a non-metal added to the catalyst (e.g., a sulfide-treatedplatinum on carbon catalyst). However, incorporation of a catalystmodifier may lead to additional impurities (e.g., leached catalystmetal) requiring removal. The catalyst modifier may also catalyze otherundesirable side-reactions, which could also introduce furtherimpurities that may require separation from the reaction mixture fromthe hydrogenation step or subsequent process steps. Avoiding the use ofadditional catalyst modifiers can also reduce catalyst cost.

Advantageously, the hydrogenation catalyst used in hydrogenationprocesses of the present invention can be essentially free or free ofmodifiers. In other words, the hydrogenation catalyst used inhydrogenation processes of the present invention can be an unmodifiedhydrogenation catalyst. As used herein, the term “modifier” refers to anadditional component that is added to the catalyst. Thus, the term“unmodified hydrogenation catalyst” does not refer to a catalyst thathas been altered by processes, such as calcination, that do notintroduce one or more additional components to the catalyst.

Catalyst modifiers include various metal promoters. Accordingly, invarious embodiments, the hydrogenation catalyst can be a non-promotedcatalyst. That is, metal promoters (or dopants) are not required and canbe avoided for various processes of the present invention. In variousembodiments, the metal promoters are transition metals. For example, themetal promoters can be selected from the group consisting of copper,nickel, iron, and combinations thereof. In these and other embodiments,the metal promoters can be alkali and alkali earth metals. As usedherein, the term “metal” includes various forms of the metal includingelemental, metal oxide, metal hydroxides, metal ions, etc.

However, certain trace metals (i.e., metals besides platinum) may bepresent as impurities in the carbon support, impurities in the platinumdeposited on the support, and/or impurities in the feed mixture (e.g.,metal leached from reaction vessels/piping or upstream catalysts). Invarious embodiments, the trace metal content of the hydrogenationcatalyst is no greater than about 0.1 wt. %, no greater than about 0.05wt. %, no greater than about 0.01 wt. %, no greater than about 0.005 wt.%, or no greater than about 0.001 wt. % of the total weight of thecatalyst. The trace metal content of the hydrogenation catalyst can befrom about 0.0001 wt. % to about 0.1 wt. %, from about 0.0001 wt. % toabout 0.05 wt. %, from about 0.0001 wt. % to about 0.01 wt. %, fromabout 0.0001 wt. % to about 0.005 wt. %, or from about 0.0001 wt. % toabout 0.001 wt. % of the total weight of the catalyst.

The hydrogenation catalyst used in processes of the present inventioncan also be essentially free or free of other non-metal catalystmodifiers (e.g., catalyst poisons). For example, the hydrogenationcatalyst can be free or essentially free of non-metal catalyst modifierssuch as sulfide.

In various embodiments, the hydrogenation catalyst that is introducedinto the hydrogenation zone consists or consists essentially of platinumon a carbon support. A catalyst that “consists essentially of” a carbonsupport and platinum would therefore include all components and minorsubstituents of the carbon support (typically an activated carbonsupport) plus the deposited platinum active phase. But, this catalystdoes not include any further catalyst modifier deposited on the carbonsupport surface intended to form a catalytically active phase or modifythe catalytically active phase.

Hydrogenation Reaction

The reaction mixture generally comprises hydrogen and thehalonitroaromatic reactant (e.g., 2,5-dichloronitrobenzene). Similar tothe hydrogenation catalyst, the feed mixture comprising thehalonitroaromatic reactant (and reaction mixture) can be essentiallyfree or free of additives that function as dehalogenation suppressors.Dehalogenation suppressors include for example, hydroxides or oxides ofmagnesium, cycloaliphatic amines such piperazine and morpholine, acidicphosphorous compounds, among others. Thus, various processes of thepresent invention comprise feeding hydrogen and a feed mixturecomprising a halonitroaromatic compound such as 2,5-dichloronitrobenzeneto a hydrogenation zone; and reacting the halonitroaromatic compound(e.g., 2,5-dichloronitrobenzene) with hydrogen in the presence of aheterogeneous hydrogenation catalyst to produce a reaction productcomprising a haloaminoaromatic compound (e.g., 2,5-dichloroaniline),wherein the hydrogenation catalyst is an unmodified hydrogenationcatalyst and the feed mixture is free of dehalogenation suppressors.

The hydrogenation reaction can be conducted with or without a solvent.In various embodiments, the feed mixture comprises a solvent (e.g.,water, alcohol, and/or acid). Thus, these processes comprise feedinghydrogen and a feed mixture comprising a halonitroaromatic compound suchas 2,5-dichloronitrobenzene and a solvent to a hydrogenation zone; andreacting the halonitroaromatic compound (e.g., 2,5-dichloronitrobenzene)with hydrogen in the presence of a heterogeneous hydrogenation catalystto produce a reaction product comprising a haloaminoaromatic compound(e.g., 2,5-dichloroaniline), wherein the hydrogenation catalystcomprises platinum on a carbon support.

In various embodiments, the solvent comprises an alcohol. One advantageof using alcohol solvents is that they are generally easier to removethan other solvents, which facilitates the isolation of reactionproduct. For example the alcohols can be methanol, ethanol, propanol,isopropanol, 1-butanol, 2-butanol, t-butanol, and mixtures thereof.

In various embodiments, the solvent comprises an acid. Without beingbound by theory, it is believed that during use of the catalyst, anacidic solvent may be beneficial in reducing the loss of selectivity todechlorination by reducing the number of small platinum particles (<2nm) on the catalyst support. Smaller platinum particles are typicallyless stable than larger platinum particles and can be more readilyleached off the carbon support in the acidic environment. Moreover, useof an acidic solvent may be beneficial if the hydrogenation process isintegrated with other process steps that also use the same solvent.

The acidic solvent can comprise an organic acid. For example, theorganic acid can be selected from the group consisting of formic acid,acetic acid, propionic acid, butyric acid, citric acid, and mixturesthereof. In certain embodiments, the organic acid comprises acetic acid.When using an acidic solvent, the acidic solvent can be from about 20wt. % to about 95 wt. %, from about 30 wt. % to about 95 wt. %, fromabout 40 wt. % to about 95 wt. %, from about 50 wt. % to about 95 wt. %,from about 60 wt. % to about 95 wt. %, or from about 70 wt. % to about95 wt. % of the feed mixture.

When using an acidic solvent such as acetic acid in the hydrogenation of2,5-dichloronitrobenzene to 2,5-dichloroaniline, a post-hydrogenationreaction between the product 2,5-dichloroaniline and acetic acid mayresult in an irreversible loss to 2,5-dichloroacetaniline. This reactionproceeds as follows:

It has been found that this loss to 2,5-dichloroacetaniline can becontrolled by subsequently cooling the reaction product to about 15° C.or less or about 10° C. or less. In various processes of the presentinvention, the reaction product is cooled to a temperature that isbetween about 0° C. and about 15° C., between about 5° C. and about 15°C., or between about 5° C. and about 10° C. (e.g., about 10° C.).

During the hydrogenation reaction, a portion of the platinum metal ofthe hydrogenation catalyst may be leached off the carbon support,especially when using an acidic solvent. Consequently, the reactionproduct can further comprise platinum. Recovery of platinum from thereaction product would further enhance process economics. Accordingly,in various embodiments, the process further comprises recoveringplatinum from the reaction product.

In the hydrogenation of 2,5-dichloronitrobenzene to 2,5-dichloroaniline,selectivity loss to 2,5-dichloroacetaniline and 2- and 3-chloroanilinehas been found to increase with high temperatures, indicating that theacetylation and dechlorination reactions become more favorable astemperature increases. Accordingly, relatively low reaction temperaturesare preferred. The hydrogenation reaction can be conducted at atemperature that is from about 20° C. to about 100° C., from about 25°C. to about 100° C., from about 40° C. to about 100° C., from about 40°C. to about 85° C., or from about 40° C. to about 70° C.

Typically, the hydrogenation reaction is conducted under a partialpressure of hydrogen that is at least about 20 kPa, at least about 100kPa, at least about 200 kPa, or at least about 500 kPa. In variousembodiments, the partial pressure of hydrogen is from about 20 kPa toabout 2000 kPa, from about 200 kPa to about 1500 kPa, or from about 500kPa to about 1000 kPa.

The hydrogenation reaction may be carried out in a wide variety ofbatch, semi-batch, and continuous reactor systems. The configuration ofthe reactor is not critical. Suitable conventional reactorconfigurations include, for example, stirred tank reactors, fixed bedreactors, trickle bed reactors, fluidized bed reactors, bubble flowreactors, plug flow reactors, buss loop reactors, and parallel flowreactors.

Process for Producing of 3,6-dichloro-2-methoxybenzoic Acid (Dicamba)

2,5-Dichloroaniline produced in accordance with any of the processesdescribed herein is a useful intermediate in the production of3,6-dichloro-2-methoxybenzoic acid (dicamba) and salts or estersthereof. International Patent Application Publication WO2015/095284,which is incorporated herein by reference, describes one process for theproduction of 3,6-dichloro-2-methoxybenzoic acid. In general, thisprocess involves diazotizing 2,5-dichloroaniline to provide2,5-dichlorobenzenediazonium. The 2,5-dichlorobenzenediazonium is thenhydrolyzed to form 2,5-dichlorophenol. Subsequently, 2,5-dichlorophenolis carboxylated to produce 2-hydroxy-3,6-dichlorobenzoic acid(3,6-dichlorosalicylic acid). This intermediate can then be methylatedto form a methylation reaction product comprising3,6-dichloro-2-methoxybenzoic acid salt and/or ester thereof. Themethylation product can then be saponified to3,6-dichloro-2-methoxybenzoic acid. Thus, the hydrogenation processes ofthe present invention can be further combined with various processes forproducing 3,6-dichloro-2-methoxybenzoic acid.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present invention.

Example 1: Calcination of Platinum-On-Carbon Catalyst

A 1 wt. % platinum on activated carbon (Pt/C) catalyst was calcined attemperature of 900° C. in a heating tube under an argon atmosphere forapproximately two hours. Subsequently, the catalyst was removed from theheating tube and mixed to minimize any non-uniform temperaturedistribution along the tube. Then, the catalyst was reloaded back intoheating tube for a second heat treatment at 900° C. for approximatelytwo hours. Alternatively, the catalyst can be calcined in a rotator tubeto achieve the uniform temperature.

The catalyst surface was imaged before and after the calcination usingscanning transmission electron microscopy (STEM). FIG. 1 presents aseries of images for the catalyst surface of a commercial Pt/C catalystprior to calcination. FIGS. 2 and 3 present a series of images for thecatalyst surface of a commercial Pt/C catalyst after calcination. Theseimages show that the calcination enhanced the sintering andagglomeration of small platinum particles (<2 nm), which appears to haveincreased the proportion of larger platinum particles (>2 nm).

Example 2: Hydrogenation of 2,5-Dichloronitrobenzene to2,5-Dichloroaniline Over Noble Metal Catalyst (General Procedure)

A general procedure for the hydrogenation of 2,5-dichloronitrobenzene to2,5-dichloroaniline was followed for each cycle. A noble metal (e.g.,platinum or palladium) supported catalyst was loaded into a HASTELLOYautoclave reactor (approx. 300 ml) and then the reactor was sealed. Asolution of 2,5-dichlorobezene (10 to 30 wt. %) in acetic acid wasintroduced to the reactor through the inlet and the system was checkedfor any leaks. The system was purged with nitrogen (i.e., pressurizingthe reactor to 239 kPa (20 psig) with nitrogen followed by purging) forthree times. After purging, the reactor was pressurized with 239 kPa (20psig) of nitrogen, and both stirring (1400 rpm) and heating werestarted. Once the temperature of the mixture reached the desiredtemperature (e.g., approximately 65° C.), stirring was stopped and thenitrogen was purged. The reactor was then charged with hydrogen gas(e.g., to a pressure of 687 kPa (85 psig)) and stirring (1400 rpm) wasrestarted. At the end of the reaction, the heating was stopped and thehydrogen in the system was purged. The system was then purged withnitrogen for three times using the same protocol as described above. Thereaction mixture was drained through the outlet into a container througha filter. The next cycle was repeated by reloading the2,5-dichlorobezene solution in acetic acid into the system containingthe Pt/C catalyst for hydrogenation.

The reaction mixture collected was analyzed for 2,5-dichloroaniline(2,5-DCA); 2,5-dichloroacetaniline (2,5-DCAN); 2-chloroaniline (2-CA);and 3-chlroaniline (3-CA) by a RP-HPLC method.

Parameters of the hydrogenation reaction were varied as described in thefollowing Examples. For example, the catalyst metal, the catalystsupport, the catalyst loading ranged from 100 mg to 800 mg, reactiontemperature ranged from 45° C. to 65° C., hydrogen pressure ranged from377 kPa (40 psig) to 1273 kPa (170 psig), and the concentration of the2,5-dichlorobezene solution in acetic acid ranged from 10 wt. % to 30wt. %.

Example 3: Effect of Catalyst Metals and Supports

The hydrogenation procedure of Example 2 was conducted with a variety ofcatalysts containing different metals (platinum and palladium) andcatalyst supports (carbon and silica). The catalysts were 1 wt. % Pt/C,1 wt. % Pt/SiO₂, 1 wt. % Pd/C, and a 5 wt. % Pt/C promoted with 0.5 wt.% Fe (5 wt. % Pt/0.5 wt. % Fe/C). These catalysts were not calcined,with the exception of the 5 wt. % Pt/0.5 wt. % Fe/C catalyst. The 5 wt.% Pt/0.5 wt. % Fe/C catalyst was calcined at a high temperature(approximately 900° C.) prior to use. In each run of the hydrogenationreaction procedure, approximately 755 mg (dry basis) of each catalystand 150 g of a 30 wt. % 2,5-dichloronitrobenzene in acetic acid wereloaded into the reactor. Hydrogen was charged to the reactor at apressure of 687 kPa (85 psig). The reactor was heated to a temperatureof 45° C. The results of these runs after one reaction cycle areprovided in Table 1.

TABLE 1 Metal and Support of Catalyst vs. Dechlorination Catalyst Lot #Lot 1 Lot 2 Metal Pt Pd Pt Pt Pt—Fe Metal Loading (wt. %) 1% 1% 1% 1%5%/0.5% Catalyst Support SiO₂ Carbon Carbon Carbon Carbon 2,5-DCAN (mol.%) 0.19 0.19 0.12 0.11 0.09 2-CA + 3-CA 0.44 2.98 0.71 0.60 0.15 (mol.%) 3-CA/2-CA Ratio 6.00 1.20 4.10 3.70 0.85 Reaction time (min) 202 29164 68 62 Conversion (%) 90.0 98.9 99.8 99.8 99.7

Among the catalysts used, both the Pd/C and Pt/SiO₂ catalysts wereobserved to be less favored for the hydrogenation reaction. The Pd/Ccatalyst was relatively less active for converting2,5-dichloronitrobenzene to 2,5-dichloroaniline by hydrogenation, asdemonstrated that the reaction was completed in much longer time (i.e.,about 300 minutes) and the loss to chloroaniline (i.e., approximately 3mol. %) was significantly higher compared to platinum catalysts. ThePt/SiO₂ catalyst was also less active, as demonstrated by the conversionof about 90% after 200 minutes. In addition, this type of Pt/SiO₂catalyst disintegrated in the reaction mixture. As a result, aconsiderable amount of catalyst material passed through the reactorfrits and collected in the reaction product. The catalyst loss on eachcycle was much higher for the Pt/SiO₂ catalyst as compared to the othercatalysts on carbon support (i.e., about 12% vs. about 5%). Because oflonger reaction time with the Pd/C and Pt/SiO₂ catalysts, theselectivity loss to 2,5-dichloroacetaniline (2,5-DCAN) was observed tobe higher as compared to the Pt/C catalysts.

The 1 wt. % Pt/C catalysts were much more active compared to the 1 wt. %Pd/C and 1 wt. % Pt/SiO₂ and had a similar activity to the 5 wt. %Pt/0.5 wt. % Fe/C catalyst, as indicated by the reaction time to achieveat least about 99% conversion. However, the selectivity loss to2-chloroaniline and 3-chloroaniline was significantly higher with thePt/C catalyst as compared to the 5 wt. % Pt/0.5 wt. % Fe/C catalyst.Furthermore, dechlorination, particularly at the ortho-position of the2,5-dichloroaniline product (resulting in 3-CA) was increased with theplatinum-only catalysts (including Pt/SiO₂), as indicated by theincreased ratio of 3-CA/2-CA. The greater selectivity loss towards 2- or3-chloroanilines using these catalysts could be due to the presence ofsmaller sized platinum particles (<2 nm) on the carbon support which arethought to favor the formation of monochloroaniline.

The 5 wt. % Pt/0.5 wt. % Fe/C catalyst was evaluated for thehydrogenation reaction. This catalyst was calcined at a high temperature(approximately 900° C.) prior to use. This catalyst is understood tohave larger platinum particles (e.g., average size of approx. 7 nm) thanthe other platinum catalysts listed in Table 1. This type of catalystwas observed to provide a reduced amount of selectivity loss to 2- and3-chloroaniline due to dechlorination and the highest selectivity to2-chloroaniline as indicated by a decreased ratio of 3-CA/2-CA.

Example 4: Effect of Hydrogen Pressure, Reaction Temperature, andReaction Solvent

Example 2 was repeated with a commercial 1 wt. % Pt/C catalyst, whichwas used without being calcined. In these runs of the hydrogenationreaction procedure, approximately 755 mg (dry basis) of the catalyst and150 g of a 30 wt. % 2,5-dichloronitrobenzene in acetic acid were loadedinto the reactor. The amount of hydrogen charged to the reactor wasvaried between runs at pressures of 474 kPa (54 psig), 687 kPa (85psig), and 860 kPa (110 psig). The temperature of the reactor was alsovaried at either 45° C. or 65° C. The results of these runs after onereaction cycle are provided in Table 2-A.

TABLE 2-A H₂ Pressure and Reaction Temperature vs. Loss to3-Chloroaniline Reaction Reaction Temperature 3-CA time Cycle # H₂Pressure (° C.) (mol. %) (Minute) 1 474 kPa (54 psig) 65 0.29 93 2 474kPa (54 psig) 45 0.21 95 3 860 kPa (110 psig) 65 0.59 31 4 860 kPa (110psig) 45 0.36 42 5 687 kPa (85 psig) 45 0.32 57 6 687 kPa (85 psig) 650.56 41

Higher hydrogen pressure and higher reaction temperature accelerated thehydrogenation reaction, but dechlorination to 3-chloroaniline was alsofavored. Therefore, the hydrogen pressure of 87 kPa (85 psig) and thereaction temperature of 45° C. were selected for the further evaluation.

In another set of experiments, Example 2 was repeated with a commercial1 wt. % Pt/C catalyst, which was used without being calcined; and thereaction solvent was varied between runs. In these runs of thehydrogenation reaction procedure, approximately 755 mg (dry basis) ofthe catalyst and 150 g of a 30 wt. % 2,5-dichloronitrobenzene in asolvent (i.e., either acetic acid or methanol) were loaded into thereactor. The amount of hydrogen charged to the reactor was 687 kPa (85psig), and the temperature of the reactor was at 45° C. The results ofthese runs after three reaction cycles are provided in Table 2-B.

TABLE 2-B Reaction Solvent vs. Dechlorination and Reaction time 2-CA +Reaction 3-CA 3-CA 3-CA/2-CA time Solvent Cycle # (mol. %) (mol. %)Ratio (Minute) Acetic 1 0.71 0.57 4.10 64 Acid 2 0.58 0.45 3.49 59 30.64 0.50 3.77 59 Methanol 1 1.13 0.94 4.91 35 2 0.91 0.77 5.49 32 31.07 0.90 5.22 30

The hydrogenation in non-acetic solvent, for example, in methanol, wasobserved to provide increased dechlorination and reduced reaction time.The higher solubility of hydrogen in methanol than in acetic acid mayresult in shorter reaction time and more dechlorination. Since the2,5-dichloroacetaniline (2,5-DCAN) is only formed in acetic acid, it canbe eliminated by using methanol as the reaction solvent.

Example 5: Effect of Calcination on Platinum Catalyst

Example 2 was repeated using calcined and un-calcined 1 wt. % Pt/Ccatalysts. The 1 wt. % Pt/C catalyst was a commercial Pt/C catalyst.Calcination was performed in accordance with the procedure described inExample 1, except that the calcination temperature was varied (e.g.,500° C., 700° C., and 900° C.). In these runs of the hydrogenationreaction procedure, approximately 755 mg (dry basis) of the catalyst and150 g of a 30 wt. % 2,5-dichloronitrobenzene in acetic acid were loadedinto the reactor. Hydrogen was charged to the reactor at a pressure of687 kPa (85 psig). The reactor was heated to a temperature of 45° C. Theresults of these runs after one reaction cycle are provided in Table 3.

TABLE 3 Catalyst Calcination Temperature vs. Impurity Profile andCatalyst Activity Catalyst Lot 1 Lot 2 Lot 1 Lot 1 Lot 2 Calcinationnone none 500 700 900 Temperature (° C.) 2,5-DCAN (mol. %) 0.12 0.110.07 0.12 0.13 2-CA + 3-CA (mol. %) 0.71 0.60 0.44 0.25 0.19 2-CA (wt.%) 0.028 0.023 0.026 0.019 0.018 3-CA/2-CA Ratio 4.1 3.7 2.6 1.7 1.1Reaction time (min) 64 68 64 74 102 Conversion (%) 99.8 99.8 99.8 99.799.5

The selectivity loss to 2,5-dichloroacetaniline (2,5-DCAN) was observedto be constant regardless of the temperature of calcination of thecatalyst. The selectivity loss to 2- and 3-chloroaniline upondechlorination of 2,5-dichloroaniline decreased considerably as thecalcination temperature increased. Furthermore, the 2-chloroanilinelevel was maintained relatively constant while the 3-chloroaniline wasobserved to be significantly less, which resulted in a decrease in theratio of 3-chloroaniline to 2-chloroaniline (3-CA/2-CA). Thisobservation is consistent with the theory that the increase of the sizeof platinum particles decreases the dechlorination, particularly at theortho-position of the 2,5-dichloroaniline product. However, the activityof the catalyst decreased slightly as the temperature of the calcinationtemperature increased as indicated by the longer reaction time.

Example 6: Comparison of Various Platinum Catalysts

Example 2 was repeated using a variety of Pt/C catalysts. The catalystswere a 1 wt. % Pt/C catalyst (used without being calcined), a 1 wt. %Pt/C catalyst that was calcined at 500° C., a 1 wt. % Pt/C catalyst thatwas calcined at 700° C., a 1 wt. % Pt/C catalyst that was calcined at900° C., and a 5 wt. % Pt/C catalyst promoted with 0.5 wt. % Fe that wascalcined at 900° C. The 1 wt. % Pt/C catalyst was a commercial Pt/Ccatalyst.

In each run of the hydrogenation reaction procedure, approximately 755mg (dry basis) of each catalyst and 150 g of a 30 wt. %2,5-dichloronitrobenzene in acetic acid were loaded into the reactor.Hydrogen was charged to the reactor at a pressure of 687 kPa (85 psig).The reactor was heated to a temperature of 45° C. The results of theseruns after a series of reaction cycles are provided in Table 4.

TABLE 4 Catalyst Varieties, Reaction Cycles vs. Dechlorination CatalystPt/C Pt/C Pt/C Pt/C Pt/Fe/C Pt/C Pt/C Pt/C Calcination Temperature (°C.) # of none 500 700 900 900 none 700 900 Cycle 2-CA + 3-CA (mol. %)3-CA/2-CA Ratio 1 0.60 0.44 0.25 0.19 0.15 3.72 1.66 1.08 2 0.55 0.350.22 0.16 0.16 3.71 1.57 1.02 3 — 0.34 0.22 — — — 1.47 — 4 — — — — — — —— 5 0.59 — 0.21 0.16 0.16 3.56 1.36 0.93 6 — — — — — — — — 7 — — — — — —— — 8 0.57 — 0.19 0.16 0.16 3.23 1.07 0.91 9 — — — — — — — — 10 — — — —— — — — 11 — — — 0.14 0.15 — — 0.94 12 0.53 — 0.16 — — 2.68 0.90 — 13 —— — — — — — — 14 — — — — — — — — 15 — — 0.14 0.12 — 2.39 0.81 0.88 16 —— — — — — — — 17 0.52 — — — — 2.25 — — 18 — — — — — — — — 19 — — — — — —— — 20 0.45 — — — — 1.99 — —

Selectivity to the preferred dechlorination compound 2-chloroanilineover a number of reaction cycles increased with increasing calcinationtemperature as indicated by a decreased ratio of 3-CA/2-CA. The 1 wt. %Pt/C catalyst that was calcined at 900° C. provided similar selectivityto the preferred dechlorination compound 2-chloroaniline as compared tothe 5 wt. % Pt/0.5 wt. % Fe/C catalyst.

To evaluate the stability of a calcined catalyst in the reaction medium,the 1 wt. % Pt/C catalyst that was calcined at 900° C. was imaged usingSTEM before the first reaction cycle (i.e., fresh catalyst) and thenagain after 15 cycles. FIGS. 2 and 3 present a series of images for thecatalyst surface after calcination, but prior to use. FIGS. 4 and 5present a series of images for the catalyst surface after 15 reactioncycles. These images show that the catalyst is stable (e.g., resistantto leaching) over the course of numerous reaction cycles.

Example 7: Preparation of 1 wt. % Platinum Catalyst on Activated Carbon(General Procedure)

The following are general procedures for the preparation of a 1 wt. %Pt/C catalyst. The carbon slurry concentration, pH adjustment, theamount of reducing agent (NaBH₄), the temperature, and the final pH ofthe slurry can vary during the process of the preparation. The followingmethods (Ia, Ib, II, III, IV, V, VI, VII, VIIIa, VIIIb, IX, Xa and Xb)are representative procedures with several variable parameters.

A. Method Ia

Activated carbon (15.0 g) was suspended to form a slurry in de-ionizedwater (approx. 150 mL) with stirring for about 20 minutes. The pH of theresulting slurry was pH 8.48. A solution of H₂PtCl₆.6H₂O (0.40 g) inde-ionized water (approx. 15 mL) was added dropwise to the carbon slurryover a period of about 15 minutes. The pH of the resulting slurrydropped to pH 5.17 upon the completion of addition of the platinumsolution. The resulting slurry was stirred for another 30 minutes atambient temperature. The pH was adjusted to about pH 4.50 with 1 M HClsolution. The slurry was then heated to 60° C. over approximately 30minutes while the pH was maintained at about pH 4.50 by addition of 1 MNaOH solution. Upon reaching the temperature of 60° C., the pH of theslurry was increased by an increment of 0.5 every 5 minutes withaddition of 1 M NaOH solution until about pH 6.00. The stirring of theslurry was continued for 10 minutes at 60° C. and pH 6.0, and thencooled to below approximately 50° C. A solution of NaBH₄ in 14 M NaOH(12 wt. %, 0.50 g) was diluted to 5 mL with de-ionized water; and thediluted solution was added dropwise to the aforementioned preparedslurry over 5 minutes. The stirring was continued for another 10 minutesafter the addition, and then heated to approximately 50° C. with anending pH of 8.49. After filtration, the wet cake was washed withde-ionized water (4×300 mL) at 50° C. while pH became 7.51, followed byanother optional wash with water (1×300 mL). The catalyst cake was thendried at approximately 110° C. under vacuum for 10 hours to provide thedried 1 wt. % Pt/C catalyst (14.8 g).

B. Method Ib (No NaBH₄ Reduction)

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approx. 140 mL) with stirring for about 20 minutes. The pH of theresulting slurry was pH 7.78. A solution of H₂PtCl₆.6H₂O (0.41 g) inde-ionized water (approx. 15 mL) was added dropwise to the carbon slurryover a period of about 17 minutes. The pH of the resulting slurrydropped to pH 3.67 upon the completion of addition of the platinumsolution. The resulting slurry was stirred for another 28 minutes atambient temperature and the pH rose to about pH 4.25. The slurry wasthen heated to 60° C. over approximately 30 minutes while the pH wasmaintained at about pH 4.00 by addition of 1 M NaOH solution. Uponreaching the temperature of 60° C., the pH of the slurry was increasedby an increment of 0.5 every 5 minutes with addition of 1 M NaOHsolution until about pH 6.00. The stirring of the slurry was continuedfor 10 minutes at 60° C. and pH 6.0. The solution was then cooled toapproximately 50° C. and the solution had pH 6.08. The pH of the slurryrose gradually to 7.65 while it continued to cool to approximately 43°C. It was then heated to approximately 55° C. in 14 minutes with anending pH of 8.99. After filtration, the wet cake was washed withde-ionized water (4×300 mL) at 50° C. The catalyst cake was then driedat approximately 110° C. under vacuum for 10 hours to provide the dried1 wt. % Pt/C catalyst (15.3 g).

C. Method II

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 120 mL) with stirring for about 40 minutes. The pHof the resulting slurry was adjusted to pH 8.33 by addition of 1M NaOHsolution. A solution of H₂PtCl₆.6H₂O (0.40 g) in de-ionized water(approximately 10 mL) was added dropwise to the carbon slurry over aperiod of about 8 minutes. The pH of the resulting slurry dropped to pH3.60 upon the completion of addition of the platinum solution. Theresulting slurry was stirred for another 10 minutes at ambienttemperature and the pH rose to pH 4.05. The pH was then adjusted toabout pH 5.0 with 1M NaOH and the resulting solution was stirred foranother 8 minutes. The slurry was then heated to 60° C. over about 15minutes while the pH was maintained at about pH 5.0 by addition of 1 MNaOH solution. Upon reaching the temperature of 60° C. for 5 minutes,the pH of the slurry was increased to about pH 6.0 with addition of 1 MNaOH solution and was maintained for 10 minutes. The pH of the slurrywas increased again to about pH 6.5 and was maintained for another 10minutes. The resulting slurry was then cooled to below about 50° C. inabout 10 minutes. A solution of NaBH₄ in 14 M NaOH (12 wt. %, 0.50 g)was diluted to 5 mL with de-ionized water; and the diluted solution wasadded dropwise to the aforementioned prepared slurry over 5 minutes. Thestirring was continued for another 5 minutes after the addition, and theresulting pH of the slurry rose to pH 8.41. The slurry was then heatedto about 57° C. over about 10 minutes with an ending pH of 9.16. Afterfiltration, the wet cake was washed with de-ionized water (4×350 mL) at50° C. with a final pH of 6.03. The catalyst cake was then dried atabout 110° C. under vacuum for 10 hours to provide the dried 1 wt. %Pt/C catalyst (15.3 g).

D. Method III

Activated carbon (15.5 g) was suspended to form slurry in de-ionizedwater (approximately 120 mL) with stirring for about 45 minutes. The pHof the resulting slurry was adjusted to pH 9.00 by addition of 1M NaOHsolution. A solution of H₂PtCl₆.6H₂O (0.41 g) in de-ionized water(approximately 10 mL) was added dropwise to the carbon slurry over aperiod of about 8.5 minutes. The pH of the resulting slurry dropped topH 3.99 upon the completion of addition of the platinum solution. Theresulting slurry was stirred for another 20 minutes at ambienttemperature and the pH rose to pH 4.77. The pH was then adjusted toabout pH 5.0 with 1M NaOH. The slurry was then heated to 60° C. overabout 15 minutes while the pH was maintained at about pH 5.0 by additionof 1 M NaOH solution. Upon reaching the temperature of 60° C. for 5minutes, the pH of the slurry was increased to about pH 6.0 withaddition of 1 M NaOH solution and was maintained for 10 minutes. The pHof the slurry was increased again to about pH 6.5 and was maintained foranother 10 minutes. The resulting slurry was then cooled to below about50° C. in about 15 minutes. A solution of NaBH₄ in 14 M NaOH (12 wt. %,0.52 g) was diluted to 5 mL with de-ionized water; and the dilutedsolution was added dropwise to the aforementioned prepared slurry over 5minutes. The stirring was continued for another 5 minutes after theaddition, and the resulting pH of the slurry rose to pH 8.14. The slurrywas then heated to about 55° C. over about 10 minutes with an ending pHof 8.94. After filtration, the wet cake was washed with de-ionized water(4×350 mL) at 50° C. with a final pH of 6.38. The catalyst cake was thendried at about 110° C. under vacuum for 10 hours to provide the dried 1wt. % Pt/C catalyst (15.2 g).

E. Method IV

Activated carbon (15.6 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) with stirring for about 27 minutes. The pHof the resulting slurry was adjusted to pH 8.50 by addition of 1M NaOHsolution. A solution of H₂PtCl₆.6H₂O (0.41 g) in de-ionized water(approximately 10 mL) was added dropwise to the carbon slurry over aperiod of about 12 minutes with co-addition of 1M NaOH. The pH of theresulting slurry dropped to pH 4.57 upon the completion of addition ofthe platinum solution. The resulting slurry was stirred for another 30minutes at ambient temperature and the pH rose to pH 5.12. The slurrywas then heated to 60° C. over about 14 minutes while the pH dropped topH 4.11. Upon reaching the temperature of 60° C., the pH of the slurrywas maintained at about pH 4.1 for 15 minutes with addition of 1 M NaOHsolution. Subsequently, the pH was increase to about pH 4.5 and wasmaintained for another 10 minutes. The pH of the slurry was increased byan increment of 0.5 every 10 minutes with addition of 1 M NaOH solutionuntil about pH 6.0. The stirring of the slurry was continued for 10minutes at 60° C. and pH 6.0, and then cooled to about 45° C. in about15 minutes. A solution of NaBH₄ in 14 M NaOH (12 wt. %, 0.80 g) wasdiluted to 8 mL with deionized water; and the diluted solution was addeddropwise to the aforementioned prepared slurry over 8 minutes. Thestirring was continued for another 12 minutes after the addition, andthe resulting pH of the slurry rose to pH 8.00 with a temperature of 37°C. The slurry was then heated to about 55° C. over about 16 minutes withan ending pH of 8.81. After filtration, the wet cake was washed withde-ionized water (4×350 mL) at 50° C. with a final pH of 6.40. Thecatalyst cake was then dried at about 110° C. under vacuum for 10 hoursto provide the dried 1 wt. % Pt/C catalyst (15.2 g).

F. Method V

Activated carbon (15.6 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) with stirring while the slurry was heatedto 41° C. for about 20 minutes. The pH of the resulting slurry wasadjusted to pH 9.00 by addition of 1M NaOH solution. A solution ofH₂PtCl₆.6H₂O (0.41 g) in de-ionized water (approximately 10 mL) wasadded dropwise to the carbon slurry over a period of about 11 minuteswith co-addition of 1M NaOH while maintaining the pH of the slurry toabove 6.0 and the temperature at about 41° C. The slurry was thenstirred for another 20 minutes at about 41° C. and the pH of slurry wasmaintained at pH 6.1 with co-addition of 1M NaOH if necessary. Theslurry was then heated to about 70° C. over a period of about 20 minuteswhile the pH was maintained between pH 6.1 to pH 6.2 with 1M NaOH. Uponreaching 70° C., the pH of the slurry was raised to pH 7.0 with 1M NaOHsolution and maintained for 10 minutes. After the slurry was cooledbelow 50° C. in about 17 minutes, a solution of NaBH₄ in 14 M NaOH (12wt. %, 1.00 g) diluted in de-ionized water (10 mL) was added dropwiseover 8 minutes. The stirring was continued for another 10 minutes afterthe addition, and the resulting pH of the slurry rose to pH 9.52 with atemperature of about 42° C. The slurry was then heated to about 60° C.in about 10 minutes with an ending pH of 9.78. After filtration, the wetcake was washed with de-ionized water (4×350 mL) at 55° C. with a finalpH of 7.90. The catalyst cake was then dried at about 110° C. undervacuum for 10 hours to provide the dried 1 wt. % Pt/C catalyst (15.2 g).

G. Method VI

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) with stirring for about 45 minutes. The pHof the resulting slurry was adjusted to about pH 6.50 by addition of 1MHCl solution. A solution of H₂PtCl₆.6H₂O (0.40 g) in de-ionized water(approximately 10 mL) was added dropwise to the carbon slurry over aperiod of about 11 minutes at ambient temperature. The pH of theresulting slurry dropped to pH 3.27 upon the completion of addition ofthe platinum solution. The resulting slurry was stirred for another 22minutes at ambient temperature and the pH rose to pH 3.65. The pH wasadjusted to pH 3.28 with 1 M HCl solution. The slurry was then stirredfor another 18 minutes and the pH of slurry ended at pH 3.54. The slurrywas then heated to about 60° C. over a period of about 15 minutes whilethe pH dropped to pH 3.13. Upon reaching 60° C., the pH of the slurrywas raised to about pH 3.5 with 1M NaOH solution and maintained for 10minutes. The pH of the slurry was increased by an increment of 0.5 every5 minutes with addition of 1 M NaOH solution until about pH 6.0. Thestirring of the slurry was continued for 10 minutes at 60° C. and pH6.0, and then cooled to below about 50° C. A solution of NaBH₄ in 14 MNaOH (12 wt. %, 0.56 g) diluted in de-ionized water (4.5 mL) was addeddropwise over 6 minutes. The stirring was continued for another 10minutes after the addition, and the resulting pH of the slurry rose topH 7.95 with a temperature of about 42° C. The slurry was then heated toabout 52° C. in about 10 minutes with an ending pH of 8.64. Afterfiltration, the wet cake was washed with de-ionized water (3×300 mL atabout 50° C., final 1×300 mL at ambient temperature) with a final pH of7.30. The catalyst cake was then dried at about 110° C. under vacuum for10 hours to provide the dried 1 wt. % Pt/C catalyst (15.2 g).

H. Method VII

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approx. 110 mL) with stirring for about 30 minutes. The pH of theresulting slurry was pH 7.73. A solution of H₂PtCl₆.6H₂O (0.40 g) inde-ionized water (approx. 10 mL) was added dropwise to the carbon slurryover a period of about 15 minutes. The pH of the resulting slurrydropped to pH 3.48 upon the completion of addition of the platinumsolution. The resulting slurry was stirred for another 35 minutes atambient temperature and the pH of slurry rose to pH 4.03. The slurry wasthen heated to 60° C. over approximately 20 minutes while the pH wasmaintained at about pH 4.00 by addition of 1 M NaOH solution. Uponreaching the temperature of 60° C., the pH of the slurry was increasedby an increment of 0.5 every 5 minutes with addition of 1 M NaOHsolution until about pH 6.00. The stirring of the slurry was continuedfor 10 minutes at 60° C. and pH 6.0. The pH of the slurry was increasedagain to about pH 6.5 and was maintained for another 15 minutes, andthen cooled to below approximately 50° C. A solution of NaBH₄ in 14 MNaOH (12 wt. %, 0.60 g) was diluted to 10 mL with de-ionized water; andthe diluted solution was added dropwise to the aforementioned preparedslurry over 15 minutes. Upon completion of addition, the slurry washeated to approximately 52° C. with an ending pH of 8.94. Afterfiltration, the wet cake was washed with de-ionized water (3×300 mL atabout 50° C., final 1×300 mL at ambient temperature) with a final pH of7.45. The catalyst cake was then dried at approximately 110° C. undervacuum for 10 hours to provide the dried 1 wt. % Pt/C catalyst (15.3 g).

I. Method VIIIa

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) containing 1,4-cyclohexanedimethanol (CHDM)(1.19 g) with stirring while the slurry was heated to 45° C. for about40 minutes. The pH of the resulting slurry was adjusted to pH 7.45 byaddition of 1M NaOH solution. A solution of H₂PtCl₆.6H₂O (0.41 g) inde-ionized water (approx. 10 mL) was added dropwise to the carbon slurryover a period of about 13 minutes at the temperature of about 43° C. to44° C. The pH of the resulting slurry dropped to pH 3.06 upon thecompletion of addition of the platinum solution. The pH of slurry wasadjusted to pH 3.50 and the resulting slurry was stirred for 5 minutesat about 43° C. The pH of slurry was raised to pH 4.00 and the resultingslurry was stirred for another 15 minutes at about 43° C. The slurry wasthen heated to 60° C. over approximately 10 minutes while the pH wasmaintained at about pH 4.00 by addition of 1 M NaOH solution. Uponreaching the temperature of 60° C., the pH of the slurry was increasedby an increment of 0.5 every 5 minutes with addition of 1 M NaOHsolution until about pH 6.00. The stirring of the slurry was continuedfor 10 minutes at 60° C. and pH 6.0. The pH of the slurry was increasedagain to about pH 6.5 and was maintained for another 15 minutes, andthen cooled to below approximately 50° C. A solution of NaBH₄ in 14 MNaOH (12 wt. %, 0.60 g) was diluted to 10 mL with deionized water; andthe diluted solution was added dropwise to the aforementioned preparedslurry over 16 minutes. Upon completion of addition, the slurry washeated to approximately 56° C. with an ending pH of 8.76. Afterfiltration, the wet cake was washed with de-ionized water (3×300 mL atabout 55° C., final 1×300 mL at ambient temperature). The catalyst cakewas then dried at approximately 110° C. under vacuum for 10 hours toprovide the dried 1 wt. % Pt/C catalyst (16.2 g).

J. Method VIIIb

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) containing 1,4-cyclohexanedimethanol (CHDM)(2.44 g) with stirring while the slurry was heated to 70° C. for about30 minutes. The pH of the resulting slurry was adjusted to pH 6.95 byaddition of 1M NaOH solution while the slurry was cooling back to 41° C.A solution of H₂PtCl₆.6H₂O (0.41 g) in de-ionized water (approx. 10 mL),pre-adjusted to about pH 1.4 with 1M NaOH solution (about 10 drops), wasadded dropwise to the carbon slurry over a period of about 14 minutes atthe temperature of about 41° C. to 42° C. The pH of the resulting slurrydropped to pH 3.60 upon the completion of addition of the platinumsolution, and the slurry was then continued to stir for 6 more minutes.The pH of slurry was adjusted to pH 4.50 and the resulting slurry wasstirred for 5 minutes at about 41° C. The pH of slurry was raised to pH5.50. The slurry was then heated to 60° C. over approximately 10 minuteswhile the pH was maintained at about pH 5.50 by addition of 1 M NaOHsolution. Upon reaching the temperature of 60° C., the pH of the slurrywas increased to about pH 6.50. The stirring of the slurry was continuedfor 15 minutes at 60-62° C. and pH 6.50, and then the solution wascooled to below approximately 50° C. A solution of NaBH₄ in 14 M NaOH(12 wt. %, 0.60 g) was diluted to 10 mL with de-ionized water; and thediluted solution was added dropwise to the aforementioned preparedslurry over 11 minutes. Upon completion of addition, the solution wascontinued for stirring for 10 minutes, and then heated to approximately53° C. over 10 minutes with an ending pH of 8.80. After filtration, thewet cake was washed with de-ionized water (3×300 mL at about 50° C.).The catalyst cake was then dried at approximately 110° C. under vacuumfor 10 hours to provide the dried 1 wt. % Pt/C catalyst (17.1 g).

K. Method IX

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) containing sucrose (1.20 g) with stirringwhile the slurry was heated to 45° C. for about 30 minutes. The pH ofthe resulting slurry was adjusted to pH 7.63 by addition of 1M NaOHsolution. A solution of H₂PtCl₆.6H₂O (0.41 g) in de-ionized water(approx. 10 mL) was added dropwise to the carbon slurry over a period ofabout 13 minutes at the temperature of about 43° C. to 44° C. The pH ofthe resulting slurry dropped to pH 3.45 upon the completion of additionof the platinum solution. At about 44° C., the pH of slurry was adjustedto pH 3.50 with stirring for 5 minutes and was then increased by anincrement of 0.5 every 10 minutes until about pH 4.50. The slurry wasthen heated to 60° C. over approximately 13 minutes while the pH wasmaintained at about pH 4.50 by addition of 1 M NaOH solution. Uponreaching the temperature of 60° C., the pH of the slurry was increasedto about pH 5.00 for 7 minutes, to pH 5.50 for 5 minutes, pH 6.00 for 10minutes, and to pH 6.50. The stirring of the slurry was continued for 15minutes at pH 6.50, and then the solution was cooled to belowapproximately 50° C. A solution of NaBH₄ in 14 M NaOH (12 wt. %, 0.60 g)was diluted to 10 mL with deionized water; and the diluted solution wasadded dropwise to the aforementioned prepared slurry over 12 minutes.Upon completion of addition, the solution was continued for stirring for10 minutes, and then heated to approximately 56° C. over 12 minutes withan ending pH of 9.10. After filtration, the wet cake was washed withde-ionized water (3×300 mL at about 50° C., final 1×300 mL at ambienttemperature). The catalyst cake was then dried at approximately 110° C.under vacuum for 10 hours to provide the dried 1 wt. % Pt/C catalyst(16.2 g).

L. Method Xa

Activated carbon (15.6 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) with stirring for about 27 minutes. The pHof the resulting slurry was adjusted to pH 8.20 by addition of 1M NaOHsolution. A solution of H₂PtCl₆.6H₂O (0.41 g) in de-ionized water(approx. 10 mL), pre-adjusted to about pH 11.4 with 1M NaOH solution(1.60 g), was added dropwise to the carbon slurry over a period of about18 minutes at ambient temperature. The pH of the resulting slurrydropped to pH 7.69 upon the completion of addition of the platinumsolution, and the slurry was then continued to stir for 18 minutes. ThepH of slurry was adjusted from pH 7.17 to pH 8.00 at about 28° C. andstirred for 2 minutes. The slurry was then heated to 60° C. overapproximately 12 minutes while the pH was maintained at about pH 8.00 byaddition of 1 M NaOH solution. Upon reaching the temperature of 60° C.,the stirring of the slurry was continued for 15 minutes, and then thesolution was cooled to below approximately 50° C. A solution of NaBH₄ in14 M NaOH (12 wt. %, 0.60 g) was diluted to 10 mL with de-ionized water;and the diluted solution was added dropwise to the aforementionedprepared slurry over 11 minutes. Upon completion of addition, thesolution was continued for stirring for 10 minutes, and then heated toapproximately 54° C. over 10 minutes with an ending pH of 9.54. Afterfiltration, the wet cake was washed with de-ionized water (3×300 mL atabout 50° C.). The catalyst cake was then dried at approximately 110° C.under vacuum for 10 hours to provide the dried 1 wt. % Pt/C catalyst(15.0 g).

M. Method Xb

Activated carbon (15.7 g) was suspended to form a slurry in de-ionizedwater (approximately 110 mL) with stirring while the slurry was heatedto 44° C. for about 34 minutes. The pH of the resulting slurry wasadjusted to pH 8.34 by addition of 1M NaOH solution. A solution ofH₂PtCl₆.6H₂O (0.41 g) in de-ionized water (approx. 10 mL) waspre-adjusted to about pH 11.8 with 1M NaOH solution (1.79 g). Theresulting platinic acid solution was added dropwise to the carbon slurryover a period of about 20 minutes at the temperature of 44-45° C. whilethe pH of the slurry was maintained at approximately pH 8.0 with 1M NaOHsolution. The pH of the resulting slurry ended with pH 8.06 upon thecompletion of addition of the platinum solution, and the slurry was thencontinued to stir for 20 minutes at pH 8.00. The slurry was then heatedto 60° C. over approximately 10 minutes while the pH was maintained atabout pH 8.00 by addition of 1 M NaOH solution. Upon reaching thetemperature of 60° C., the stirring of the slurry was continued for 20minutes, and then the solution was cooled to below approximately 50° C.A solution of NaBH₄ in 14 M NaOH (12 wt. %, 0.60 g) was diluted to 10 mLwith de-ionized water; and the diluted solution was added dropwise tothe aforementioned prepared slurry over 10 minutes. Upon completion ofaddition, the solution was continued for stirring for 10 minutes, andthen heated to approximately 54° C. over 10 minutes with an ending pH of9.61. After filtration, the wet cake was washed with de-ionized water(3×300 mL at about 50° C.). The catalyst cake was then dried atapproximately 110° C. under vacuum for 10 hours to provide the dried 1wt. % Pt/C catalyst (15.2 g).

Parameters for the process are summarized in Table 5-A and Table 5-B.

TABLE 5-A Parameters for the Preparation of 1% Pt Catalyst (Method Ia toVII) on activated carbon Method Method Method Method Method MethodMethod Conditions Ia II III IV V VI VII Amount of carbon (g) 15.0  15.7 15.5  15.6  15.6  15.7  15.7  Initial Carbon Slurry ~0.10  ~0.13  ~0.13 ~0.14  ~0.14 at ~0.14  ~0.14  concentration (g/mL) 41° C. pH of initialslurry 8.48 8.33 9.00 8.50 9.00 6.50 7.73 Amount of 0.40 0.40 0.41 0.410.41 0.40 0.40 H₂PtCl₆•6H₂O (g) pH after addition of 5.17 3.60 3.99 4.576.0 at 3.27 3.48 H₂PtCl₆•6H₂O 41° C. Temperature of the 60° C. 60° C.60° C. 60° C. 70° C. 60° C. 60° C. first heating pH range during the4.50 to 5.0 to 5.0 to 4.1 to 6.1 to 3.1 to 4.0 to first heating 6.0 6.56.5 6.0 7.0 6.0 6.5 Temperature before <50° C.  <50° C.  <50° C.  ~45°C.  <50° C.  <50° C.  <50° C.  adding reducing agent Amount of Reducing0.50 0.50 0.52 0.80 1.00 0.56 0.60 Agent (12 wt. % NaBH₄ in 14M NaOH)(g) pH after adding 7.59 8.41 8.14 8.00 9.52 7.95 8.51 NaBH₄ Temperatureof the 50° C. 57° C. 55° C. 55° C. 55° C. 52° C. 52° C. second heatingEnding pH after the 8.49 9.16 8.94 8.81 9.78 8.64 8.94 2^(nd) heating pHafter water wash 7.51 6.03 6.38 6.40 7.90 7.30 7.45 (4 x) of wet cake

TABLE 5-B Parameters for the Preparation of 1% Pt Catalyst (Method VIIIato Xb, Ib) on activated carbon Method Method Method Method Method MethodConditions VIIIa VIIIb IX Xa Xb Ib Amount of carbon (g) 15.7  15.7 15.7  15.6  15.7  15.0  Initial Carbon Slurry ~0.14 at ~0.14 at ~0.14 at~0.14  ~0.14 at ~0.11  concentration (g/mL) 45° C. 70° C. 45° C. 45° C.Pore blocking modifier CHDM CHDM Sucrose none none none (1.19 g) (2.44g) (1.20 g) pH of initial slurry 7.45 6.95 at 7.63 8.20 8.34 7.78 41° C.Amount of H₂PtCl₆•6H₂O (g) 0.41 0.41 0.41 0.41 0.41 0.41 pH adjustmentof the none pH 1.4 none pH 11.4 pH 11.8 none H₂PtCl₆•6H₂O solution pHafter addition of 3.06 3.60 3.45 7.69 8.00 3.67 H₂PtCl₆•6H₂O Temperatureof the first 60° C. 60° C. 60° C. 60° C. 60° C. 60° C. heating pH rangeduring the first 4.0 to 5.5 to 4.5 to 8.0  8.0  4.0 to heating 6.5 6.56.5 6.0 Temperature before adding <50° C.  <50° C.  <50° C.  <50° C. <50° C.  <50° C.  reducing agent Amount of Reducing 0.60 0.60 0.60 0.600.60 None Agent (12 wt. % NaBH₄ in 14M NaOH) (g) Temperature of thesecond 56° C. 53° C. 56° C. 54° C. 54° C. 55° C. heating Ending pH afterthe 2^(nd) 8.76 8.80 9.10 9.54 9.61 8.99 heating

Example 8: Long-Term Cycle Study of 1 wt. % Pt on Activated CarbonSupport

Example 2 was repeated using 1 wt. % Pt/C catalysts over a series ofreaction cycles (e.g., over 30 or 40 cycles). The first catalyst was acommercial Pt/C catalyst that was calcined at 800° C. The secondcatalyst was also a Pt/C catalyst that was calcined at 800° C. However,the second catalyst was prepared according to procedure Method Ia inExample 7. In each run of the hydrogenation reaction, approximately 755mg (dry basis) of each catalyst and 150 g of a 30 wt. %2,5-dichloronitrobenzene in acetic acid were loaded into the reactor.Hydrogen was charged to the reactor at a pressure of 687 kPa (85 psig).The reactor was heated to a temperature of 45° C. The results of theseruns over the course of a series of reaction cycle are provided in Table6.

TABLE 6 Cycles vs. Dechlorination Commercial 1 wt. % Pt/C Prepared 1 wt.% Pt/C 2-CA + Reaction 2-CA + Reaction # of 3-CA 2-CA 3-CA/2-CA time3-CA 2-CA 3-CA/2-CA time Cycle (mol. %) (mol. %) ratio (min) (mol. %)(mol. %) ratio (min) 1 0.25 0.057 3.40 44 0.13 0.032 2.97 53 2 0.220.049 3.52 53 0.11 0.025 3.34 48 5 0.23 0.064 2.60 45 0.11 0.027 3.27 478 0.23 0.062 2.70 48 0.15 0.039 2.91 44 12 0.24 0.072 2.35 50 0.13 0.0352.71 47 16 0.23 0.067 2.43 50 — — — 49 17 — — — 51 0.13 0.040 2.20 49 18— — — 52 0.13 0.040 2.16 48 19 — — — 51 0.13 0.040 2.16 44 21 0.16 0.0502.18 52 — — — 47 27 0.13 0.039 2.31 57 0.10 0.035 1.89 52 28 — — — 570.10 0.032 2.01 50 33 — — — — 0.10 0.033 1.76 52 34 — — — — 0.09 0.0331.74 52 39 — — — — 0.09 0.033 1.64 55 43 — — — — 0.08 0.032 1.63 55

Both catalysts exhibited good stability after long-term usages. Theresults confirm that the higher selectivity to the preferreddechlorination compound 2-chloroaniline was observed over the series ofcycles on both catalysts. These results are consistent with thosepresented in Example 6.

Example 9: Long-term Cycle Study of 1 wt. % Pt on Activated CarbonSupport

The catalyst surface of the prepared catalyst from Example 8 was imagedafter the calcination and after use in 43 cycles of the hydrogenationreaction using STEM. FIGS. 6 and 7 present a series of images for thecatalyst surface after calcination. FIGS. 8 and 9 present a series ofimages for the catalyst surface after 43 cycles of the hydrogenationreaction. These images show that the catalyst is stable (e.g., resistantto leaching) over the course of numerous reaction cycles.

Example 10: Analysis of Activated Carbon Supports

The activated carbon supports used for the 1 wt. % Pt/C catalyst inExample 9 and the 5 wt. % Pt/C in Example 6 were analyzed for physicalproperties such as surface area using the Langmuir nitrogen absorptionmethod. The results of the analysis are provided in Table 7. Themicropore surface area is attributable to pores that are less than 2 nm.The external surface area is attributable to pores that are greater than2 nm.

TABLE 7 Physical Properties of Activated Carbon Supports for SelectedCatalysts Total Langmuir Micropore External Average Carbon Surface AreaSurface Area Surface Area pore diameter Type (m²/g) (m²/g) (m²/g) (nm)A¹ 2704 1944 760 2.3 B² 1597 1294 303 2.0 ¹The activated carbon supportused for the 1 wt. % Pt/C catalyst in Example 9. ²The activated carbonsupport used for the 5 wt. % Pt/0.5 wt. % Fe/C catalyst in Example 6.

Example 11: Effect of Hydrogen Pressure with Calcined Platinum Catalyst

Example 2 was repeated with a 1 wt. % Pt/C catalyst that was calcined at800° C. In this run, the hydrogen pressure was increased from 687 kPa(85 psig) in reaction cycles 1 to 33 to 963 kPa (125 psig) in reactioncycles 34 to 40 while using the same bed of catalyst. A2,5-dichloronitrobenzene solution in acetic acid (30 wt. %) and areaction temperature of 45° C. were used. The results of this experimentat different cycles are provided in Table 8.

TABLE 8 Hydrogen Pressure vs. Dechlorination with Calcined PlatinumCatalyst 1 wt. % Pt/C 2-CA + Reaction # of Hydrogen 3-CA 2-CA 3-CA/2-CAtime Cycle Pressure (mol. %) (mol. %) ratio (min) 1 687 kPa 0.25 0.0573.40 44 2 (85 psig) 0.22 0.049 3.52 53 5 0.23 0.064 2.60 45 8 0.23 0.0622.70 48 12 0.24 0.072 2.35 50 16 0.23 0.067 2.43 50 17 — — — 51 18 — — —52 19 — — — 51 21 0.16 0.050 2.18 52 27 0.13 0.039 2.31 57 28 — — — 5733 — — — — 34 963 kPa 0.11 0.031 2.66 48 35 (125 psig) — — — 48 36 — — —48 37 — — — 49 38 — — — 49 39 — — — 49 40  0.081 0.022 2.72 50

The results show that higher hydrogen pressure accelerated the reactionto a degree. Also, increased hydrogen pressure slightly favored thedechlorination to 3-chloroaniline formation, as indicated by theincreased ratio of 3-CA/2-CA.

Example 12: Platinum Leaching of Catalyst During Hydrogenation

Example 2 was repeated with a 1 wt. % Pt/C catalyst (without beingcalcined) and a 1 wt. % Pt/C catalyst that was calcined at 900° C. The 1wt. % Pt/C catalyst was a commercial Pt/C catalyst. In these runs of thehydrogenation reaction procedure, approximately 755 mg (dry basis) ofthe catalyst and 150 g of a 30 wt. % 2,5-dichloronitrobenzene in aceticacid were loaded into the reactor. Hydrogen was charged to the reactorat a pressure of 687 kPa (85 psig). The reactor was heated to atemperature of 45° C. The reaction mixture at the end of hydrogenationcycles (cycle 1, 2, and 3) were evaluated for platinum leaching via aplatinum metal analysis by an Inductively Coupled Plasma (ICP) method.The results of the platinum metal analyses are provided in Table 9.

TABLE 9 ICP Metal Analysis of Reaction Product Mixture Leached Pt as apercentage of total Pt metal Hydrogenation Hydrogenation HydrogenationCatalyst Calcination Cycle 1 Cycle 2 Cycle 3 none 0.63 0.20 0.10 900° C.0.22 0.08 0.05

The calcination of the catalyst clearly decreased platinum leaching inthe reaction environment.

Example 13: Performance of Catalysts Prepared by Various Methods

Example 2 was repeated with a variety of catalysts prepared by methodsillustrated in Example 7 on activated carbon supports described inExample 10. The catalysts were either calcined at a high temperature(e.g., 800° C., 825° C., or 850° C.) or not calcined prior to use. Ineach run of the hydrogenation reaction procedure, approximately 755 mg(dry basis) of each catalyst and 150 g of a 30 wt. %2,5-dichloronitrobenzene in acetic acid were loaded into the reactor.Hydrogen was charged to the reactor at a pressure of 687 kPa (85 psig).The reactor was heated to a temperature of 65° C. The results of theseruns (average data of the first and second cycles) are provided in Table10.

TABLE 10 Performance Summary of Catalysts Prepared by Various MethodsCatalyst Calcination None Calcined Method Carbon Reaction 2-CA +Reaction 2-CA + Exp. Number Type time 3-CA Temperature time 3-CA No.(Ex. 7) (Ex. 10) (min) (mol. %) (° C.) (min) (mol. %) 13.1 Ia B 39.70.52 850° C. 49.5 0.25 13.2 Ia¹ B 39.2 0.51 850° C. 52.5 0.26 13.3 Ia A41.8 0.17 800° C. 41.9 0.08 13.4 II B 38.8 0.53 850° C. 44.9 0.23 13.5III B 38.3 0.46 850° C. 47.4 0.27 13.6 IV B 37.3 0.50 850° C. 47.5 0.2113.7 V B 37.7 0.52 850° C. 44.9 0.27 13.8 VI B 39.8 0.54 850° C. 52.00.26 13.9 VI B 39.8 0.54  850° C.³ 69.4 0.27 13.10 VII B 42.9 0.43 850°C. 48.0 0.29 13.11 VIIIb B 35.8 0.53 850° C. 67.3 0.24 13.12 IX B 38.80.54 825° C. 61.2 0.24 13.13 Xa B 35.9 0.62 850° C. 43.9 0.30 13.14 Xb B33.7 0.60 850° C. 42.8 0.29 13.15 Ib² B 62.3 0.44 800° C. 69.9 0.1613.16 Ib² B 62.3 0.44  850° C.³ 154.5 0.26 13.17 Ib² B 62.3 0.44  750°C.³ 42.4 0.66 ¹The initial pH of Method Ia was adjusted to pH 8.47; ²NoNaBH₄ reduction; ³Calcination in the presence of 5% hydrogen gas.

The selectivity loss to 2- and 3-chloroaniline upon dechlorination of2,5-dichloroaniline is dependent on the nature and the porosity of theactivated carbon support. The catalyst prepared on carbon type Aappeared to provide less dichlorinated products.

There is no significant difference of dechlorination selectivityobserved with catalysts prepared by various parameters such as pHs andtemperatures on the same type of activated carbon (e.g., Method Ia, II,III, IV, V, VI, and VII).

A slightly increased dechlorination to 2- and 3-chloroaniline wasobserved with the catalysts prepared by Method Xa and Xb, where the pHof the chloroplatinic acid solution was pre-adjusted to higher pHs(e.g., about pH 11).

A better dechlorination selectivity was achieved with the catalystprepared by Method Ib, where the plantinum precursor was not reduced.However, the activity of the catalyst was observed to be less, asrepresented as having longer reaction time. The lower activity withimproved selectivity were attributed to the excessive agglomeration ofthe platinum, which was in-situ reduced by the hydrogen during thehydrogenation reaction, resulting in an excessive Ostwald ripening typeplantinum movement. A better approach is to calcine the un-reducedplantinum precursor on carbon in an inert atmosphere at ahigh-temperature. Since metal oxides in general have higher mobility onsupport surface, the high-temperature calcination of an un-reducedplantinum precursor in an inert atmosphere will lead to more platinumagglomeration before the platinum is reduced at a high temperature(e.g., 800° C.) by the carbon. This is consistent with the results ofobserved good dechlorination selectivity (i.e., 0.16 mol %) but withlonger reaction time (i.e., 69.9 minutes).

In general, high-temperature treatment of catalysts under hydrogenatmosphere reduced the catalyst activity due to possible spillover ofcarbonaceous materials over the platinum surface.

Example 14: Performance of Catalysts Prepared by Various Methods

The catalyst surface from Exp. 13.15 (i.e., the catalyst was preparedwithout NaBH₄ reduction) of Example 13 was imaged before calcination andafter calcination (at 800° C.) using STEM. FIGS. 10 and 11 present aseries of images for the catalyst surface before calcination. FIGS. 12and 13 present a series of images for the catalyst surface aftercalcination at 800° C. These images show that the catalyst leads toplatinum agglomeration after calcinations of the un-reduced plantinumprecursor on carbon at a high temperature (e.g., 800° C.). The catalystsurface from Experiment 13.17 was also imaged after calcination (in thepresence of 5% hydrogen gas at 750° C.) using STEM. FIGS. 14 and 15present a series of images for the catalyst surface after calcinationsin the presence of 5% hydrogen gas at 750° C. These images show that thehigh-temperature treatment of catalysts under hydrogen atmospherereduces platinum agglomeration of the un-reduced plantinum precursor oncarbon.

Example 15: Hydrogenation Parameters in Various Reaction Solvents

Example 2 was repeated with a catalyst prepared by Method V of Example 7on activated carbon (type-B of Example 10), which was usedas-synthesized without being calcined; and the reaction solvent wasvaried between runs. In these runs of the hydrogenation reactionprocedure, approximately 755 mg (dry basis) of the catalyst and 150 g ofa 30 wt. % 2,5-dichloronitrobenzene in a solvent (i.e., acetic acid,isopropanol, or methanol) were loaded into the reactor. The amount ofhydrogen charged to the reactor was 687 kPa (85 psig) for runs in eitheracetic acid or isopropanol, and 584 kPa (70 psig) for runs in methanol.The temperature of the reactor was varied at 65° C. (for runs in aceticacid or isopropanol), 55° C. (for runs in isopropanol), or 45° C. (forruns in methanol). The results of these runs after nine reaction cyclesare provided in Table 11.

TABLE 11 Reaction Parameters in Various Solvents Acetic Acid IsopropanolIsopropanol Methanol (85 psig H₂, 65° C.) (85 psig H₂, 65° C.) (85 psigH₂, 55° C.) (70 psig H₂, 45° C.) 2-CA + Reaction 2-CA + Reaction 2-CA +Reaction 2-CA + Reaction 3-CA time 3-CA time 3-CA time 3-CA time Cycle #(mol. %) (min) (mol. %) (min) (mol. %) (min) (mol. %) (min) 1 0.54 39.70.50 40.8 0.39 41.8 0.58 39.7 2 0.63 36.7 0.62 36.7 0.56 39.8 0.65 34.63 0.63 39.9 0.82 36.8 0.62 40.8 0.57 39.7 4 0.58 35.6 0.93 37.7 0.3938.7 — — 5 0.62 36.6 0.89 35.7 0.54 38.6 0.51 40.8 6 0.56 35.7 0.83 36.70.64 40.9 0.50 46.0 7 0.49 35.7 0.47 34.7 0.59 40.8 0.48 42.8 8 0.5336.7 0.72 34.7 0.40 38.8 0.48 41.8 9 0.56 35.7 0.80 35.7 0.49 38.7 0.4842.8 Average 0.57 36.9 0.73 36.6 0.51 39.9 0.53 41.0

In order to have a similar performance of the catalyst in acetic acid,the reaction parameters (i.e., reaction temperature and hydrogenpressure) were adjusted for runs in either isopropanol or methanol. Thedechlorination to 2- and 3-chloroaniline in either isopropanol (at 55°C., 85 psig H₂) or methanol (45° C., 70 psig H₂) is similar to the onein acetic acid (65° C., 85 psig H₂), illustrated in Table 11. Theaverage reaction time were similar under all conditions, as of 36.9,36.6, 39.9 and 41.0 minutes for acetic acid (at 65° C., 85 psig H₂),isopropanol (at 65° C., 85 psig H₂), isopropanol (at 55° C., 85 psigH₂), and methanol (at 45° C., 70 psig H₂); respectively.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above described catalyst andprocesses without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawing[s] shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A process for producing 2,5-dichloroaniline, theprocess comprising: feeding hydrogen and a feed mixture comprising2,5-dichloronitrobenzene and a solvent comprising an acid to ahydrogenation zone; and reacting the 2,5-dichloronitrobenzene withhydrogen in the presence of a heterogeneous hydrogenation catalystcomprising platinum on a carbon support to produce a reaction productcomprising 2,5-dichloroaniline.
 2. A process for producing2,5-dichloroaniline, the process comprising: feeding hydrogen and a feedmixture comprising 2,5-dichloronitrobenzene to a hydrogenation zone; andreacting the 2,5-dichloronitrobenzene with hydrogen in the presence of aheterogeneous hydrogenation catalyst comprising platinum on a carbonsupport to produce a reaction product comprising 2,5-dichloroaniline,wherein the hydrogenation catalyst is an unmodified hydrogenationcatalyst and the feed mixture is free of dehalogenation suppressors. 3.The process of claim 1 or 2 wherein the hydrogenation catalyst is acalcined hydrogenation catalyst.
 4. A process for producing2,5-dichloroaniline, the process comprising: feeding hydrogen and a feedmixture comprising 2,5-dichloronitrobenzene to a hydrogenation zone; andreacting the 2,5-dichloronitrobenzene with hydrogen in the presence of aheterogeneous hydrogenation catalyst comprising platinum on a carbonsupport to produce a reaction product comprising 2,5-dichloroaniline,wherein the hydrogenation catalyst is a calcined hydrogenation catalyst.5. The process of claim 3 or 4 wherein the calcined hydrogenationcatalyst is prepared by heating the carbon support having platinumthereon to a temperature of at least about 500° C., at least about 600°C., at least about 700° C., at least about 800° C., or at least about900° C.
 6. The process of claim 3 or 4 wherein the calcinedhydrogenation catalyst is prepared by heating the carbon support havingplatinum thereon to a temperature of from about 500° C. to about 1000°C., from about 600° C. to about 1000° C., from about 700° C. to about1000° C., from about 800° C. to about 1000° C., from about 500° C. toabout 950° C., from about 600° C. to about 950° C., from about 700° C.to about 950° C., or from about 800° C. to about 950° C.
 7. The processof any one of claims 3 to 6 wherein the carbon support having platinumthereon is calcined in an inert, non-oxidizing atmosphere consistingessentially of inert gases selected from the group consisting ofnitrogen, noble gases, or mixtures thereof.
 8. The process of any one ofclaims 3 to 6 wherein the carbon support having platinum thereon iscalcined in a non-oxidizing atmosphere comprising from about 1% to about5% by volume hydrogen.
 9. The process of any one of claims 3 to 8wherein the carbon support having platinum thereon that is calcinedcomprises unreduced platinum.
 10. The process of claim 9 wherein thecarbon support having platinum thereon is prepared by depositing theplatinum onto the carbon support without use of a reducing agent; andcalcining the platinum on carbon support.
 11. The process of any one ofclaims 1 to 10 wherein the carbon support is a particulate.
 12. Theprocess of any one of claims 1 to 11 wherein the hydrogenation catalystcomprises platinum metal particles at the surface of the carbon supportof a size up to 10 nm in their largest dimension and no more than about50% (number basis), no more than about 25% (number basis), no more thanabout 20% (number basis), no more than about 15% (number basis), or nomore than about 10% (number basis) of the platinum metal particles areless than 2 nm in their largest dimension.
 13. The process of any one ofclaims 1 to 11 wherein the hydrogenation catalyst comprises platinummetal particles at the surface of the carbon support of a size up to 10nm in their largest dimension and at least about 25% (number basis), atleast about 40% (number basis), at least about 50% (number basis), atleast about 60% (number basis), at least about 70% (number basis), or atleast about 80% (number basis) of the platinum metal particles are from2 nm to 10 nm in their largest dimension.
 14. The process of any one ofclaims 1 to 13 wherein the hydrogenation catalyst comprises platinummetal particles of a size up to 10 nm in their largest dimension andthese particles are characterized as having an average particle size ofgreater than about 2.5 nm, greater than about 3 nm, greater than about 4nm, or greater than about 5 nm.
 15. The process of any one of claims 1to 13 wherein the hydrogenation catalyst comprises platinum metalparticles of a size up to 10 nm in their largest dimension and theseparticles are characterized as having an average particle size fromabout 2.5 to about 8 nm, from about 3 to about 7 nm, from about 3 toabout 6 nm, or from about 3 to about 5 nm.
 16. The process of any one ofclaims 1 to 15 wherein the hydrogenation catalyst has a platinum loadingthat is no greater than about 5 wt. %, no greater than about 4 wt. %, nogreater than about 3 wt. %, no greater than about 2 wt. %, no greaterthan about 1.5 wt. %, or no greater than about 1 wt. % of the totalcatalyst weight.
 17. The process of any one of claims 1 to 16 whereinthe hydrogenation catalyst has a platinum loading that is from about 0.1wt. % to about 5 wt. %, from about 0.1 wt. % to about 4 wt. %, fromabout 0.1 wt. % to about 3 wt. %, from about 0.1 wt. % to about 2 wt. %,from about 0.1 wt. % to about 1.5 wt. %, from about 0.1 wt. % to about 1wt. %, from about 0.5 wt. % to about 5 wt. %, from about 0.5 wt. % toabout 4 wt. %, from about 0.5 wt. % to about 3 wt. %, from about 0.5 wt.% to about 2 wt. %, from about 0.5 wt. % to about 1.5 wt. %, or fromabout 0.5 wt. % to about 1 wt. % of the total catalyst weight.
 18. Theprocess of any one of claims 1 to 17 wherein the hydrogenation catalystis a non-promoted catalyst.
 19. The process of claim 18 wherein themetal promoters are transition metals.
 20. The process of claim 18 or 19wherein the metal promoters are selected from the group consisting ofcopper, nickel, iron, and combinations thereof.
 21. The process of anyone of claims 18 to 20 wherein the metal catalyst modifiers are alkaliand alkali earth metals.
 22. The process of any one of claims 1 to 21wherein the trace metal content of the hydrogenation catalyst is nogreater than about 0.1 wt. %, no greater than about 0.05 wt. %, nogreater than about 0.01 wt. %, no greater than about 0.005 wt. %, or nogreater than about 0.001 wt. % of the total weight of the catalyst. 23.The process of any one of claims 1 to 21 wherein the trace metal contentof the hydrogenation catalyst is from about 0.0001 wt. % to about 0.1wt. %, from about 0.0001 wt. % to about 0.05 wt. %, from about 0.0001wt. % to about 0.01 wt. %, from about 0.0001 wt. % to about 0.005 wt. %,or from about 0.0001 wt. % to about 0.001 wt. % of the total weight ofthe catalyst.
 24. The process of any one of claims 1 to 23 wherein thehydrogenation catalyst is essentially free or free of metal catalystmodifiers.
 25. The process of any one of claim 1 or 3-24 wherein thehydrogenation catalyst is an unmodified hydrogenation catalyst.
 26. Theprocess of any one of claims 1 to 25 wherein the carbon support has atotal Langmuir specific surface area that is at least about 500 m²/g, atleast about 600 m²/g, at least about 800 m²/g, more preferably at leastabout 900 m²/g, at least about 1000 m²/g, at least about 1100 m²/g, orat least about 1200 m²/g.
 27. The process of any one of claims 1 to 25wherein the carbon support has a total Langmuir specific surface areathat is from about 500 m²/g to about 3000 m²/g, from about 750 m²/g toabout 3000 m²/g, from about 1000 m²/g to about 3000 m²/g, from about1250 m²/g to about 3000 m²/g, from about 1500 m²/g to about 3000 m²/g,from about 1500 m²/g to about 2000 m²/g, or from about 2500 m²/g toabout 3000 m²/g.
 28. The process of any one of claims 1 to 27 whereinthe carbon support has a Langmuir micropore surface area that is atleast about 750 m²/g, at least 1000 m²/g, or at least about 1250 m²/g.29. The process of any one of claims 1 to 27 wherein the carbon supporthas a Langmuir micropore surface area that is from about 750 m²/g toabout 2000 m²/g, from about 1000 m²/g to about 2000 m²/g, or from about1250 m²/g to about 2000 m²/g.
 30. The process of any one of claims 1 to29 wherein the carbon support has a Langmuir surface area attributableto pore greater than 2 nm that is from about 100 m²/g to about 1000m²/g, from about 200 m²/g to about 800 m²/g, or from about 300 m²/g toabout 800 m²/g.
 31. The process of any one of claims 1 to 30 wherein atleast about 50%, at least about 60%, at least about 70%, or at leastabout 80% of the total Langmuir surface area of the carbon support isattributable to micropores.
 32. The process of any one of claims 1 to 30wherein from about 50% to about 90%, from about 60% to about 90%, orfrom about 65% to about 85% of the total Langmuir surface area of thecarbon support is attributable to micropores.
 33. The process of any oneof claims 1 to 32 wherein the carbon support has an average porediameter that is in the range of from about 0.5 nm to about 5 nm, fromabout 1 nm to about 5 nm, from 1 nm to about 4 nm, from about 1 nm toabout 3 nm, or from about 2 nm to about 5 nm.
 34. The process of any oneof claims 1 to 33 wherein the carbon support has a pore volume of atleast about 0.3 ml/g, at least about 0.4 ml/g, or at least about 0.5ml/g.
 35. The process of any one of claims 1 to 34 wherein the carbonsupport has a pore volume of from about 0.1 to about 2.5 ml/g, fromabout 0.2 to about 2.0 ml/g, or from about 0.4 to about 1.5 ml/g. 36.The process of any one of claims 1 to 34 wherein the carbon support hasa pore volume that is from about 0.3 ml/g to about 0.1 ml/g, or fromabout 0.5 ml/g to about 0.1 ml/g that is attributable to pores of adiameter from 0.5 nm to 5 nm.
 37. The process of any one of claims 1 to36 wherein the carbon support of the hydrogenation catalyst comprisesactivated carbon.
 38. The process of any one of claims 1 to 37 whereinthe hydrogenation catalyst that is introduced into the hydrogenationzone consists essentially of platinum on a carbon support.
 39. Theprocess of any one of claims 2 to 38 wherein the feed mixture furthercomprises a solvent.
 40. The process of claim 39 wherein the solventcomprises an alcohol.
 41. The process of claim 40 wherein the alcohol isselected from the group consisting of methanol, ethanol, propanol,isopropanol, 1-butanol, 2-butanol, t-butanol, and mixtures thereof. 42.The process of any one of claims 39 to 41 wherein the solvent comprisesan acid.
 43. The process of claim 1 or 42 wherein the acid comprises anorganic acid.
 44. The process of claim 43 wherein the organic acid isselected from the group consisting of formic acid, acetic acid,propionic acid, butyric acid, citric acid, and mixtures thereof.
 45. Theprocess of claim 43 wherein the organic acid comprises acetic acid. 46.The process of claim 45 wherein the reaction product further comprises2,5-dichloroacetaniline.
 47. The process of any one of claims 1 to 46wherein the acidic solvent is from about 20 wt. % to about 95 wt. %,from about 30 wt. % to about 95 wt. %, from about 40 wt. % to about 95wt. %, from about 50 wt. % to about 95 wt. %, from about 60 wt. % toabout 95 wt. %, or from about 70 wt. % to about 95 wt. % of the feedmixture.
 48. The process of any one of claims 1 to 47 wherein thehydrogenation reaction is conducted at a temperature that is from about20° C. to about 100° C., from about 25° C. to about 100° C., from about40° C. to about 100° C., from about 40° C. to about 85° C., or fromabout 40° C. to about 70° C.
 49. The process of any one of claims 1 to48 wherein hydrogenation reaction is conducted under a partial pressureof hydrogen that is at least about 20 kPa, at least about 100 kPa, atleast about 200 kPa, or at least about 500 kPa.
 50. The process of anyone of claims 1 to 49 wherein hydrogenation reaction is conducted undera partial pressure of hydrogen that is from about 20 kPa to about 2000kPa, from about 200 kPa to about 1500 kPa, or from about 500 kPa toabout 1000 kPa.
 51. The process of any one of claims 1 to 50 furthercomprising cooling the reaction product comprising 2,5-dichloroanilineto a temperature that is about 15° C. or less or about 10° C. or less.52. The process of any one of claims 1 to 51 further comprising coolingthe reaction product comprising 2,5-dichloroaniline to a temperaturethat is between about 0° C. and about 15° C., between about 5° C. andabout 15° C., or between about 5° C. and about 10° C.
 53. The process ofany one of claims 1 to 52 wherein the feed mixture is free oressentially free of additives that function as dehalogenationsuppressors.
 54. The process of any one of claims 1 to 53 wherein thefeed mixture is free or essentially free of hydroxides or oxides ofmagnesium, cycloaliphatic amines, and acidic phosphorous compounds. 55.The process of any one of claims 1 to 54 wherein the reaction productfurther comprises 2-chloroaniline and 3-chloroaniline.
 56. The processof claim 55 wherein the mole ratio of 3-chloroaniline to 2-chloroanilineis no greater than about 6:1, no greater than about 5:1, no greater thanabout 4:1, no greater than about 3:1, no greater than about 2:1, or nogreater than about 1:1.
 57. The process of claim 55 wherein the moleratio of 3-chloroaniline to 2-chloroaniline is from about 0.5:1 to about6:1, from about 0.5:1 to about 5:1, from about 0.5:1 to about 4:1, fromabout 0.5:1 to about 3:1, from about 0.5:1 to about 2:1, from about 1:1to about 6:1, from about 1:1 to about 5:1, from about 1:1 to about 4:1,from about 1:1 to about 3:1, or from about 1:1 to about 2:1.
 58. Theprocess of any one of claims 55 to 57 wherein the loss of selectivityfrom 2,5-dichloroaniline to 2-chloroaniline and 3-chloroaniline is lessthan about 0.4 mol. %, less than about 0.3 mol. %, or less than about0.2 mol. %.
 59. The process of any one of claims 1 to 57 wherein theyield of 2,5-dichloroaniline is at least about 90%, at least about 92%,at least about 95%, at least about 98%, or at least about 99%.
 60. Theprocess of any one of claims 1 to 59 wherein the reaction productfurther comprises platinum.
 61. The process of claim 60 wherein theprocess further comprises recovering platinum from the reaction product.62. A process for preparing 3,6-dichloro-2-methoxybenzoic acid or saltor ester thereof, the process comprising: producing 2,5-dichloroanilineaccording to any one of claims 1 to 61; diazotizing 2,5-dichloroanilineto provide 2,5-dichlorobenzenediazonium; hydrolyzing2,5-dichlorobenzenediazonium to form 2,5-dichlorophenol; carboxylating2,5-dichlorophenol to form 2-hydroxy-3,6-dichlorobenzoic acid;methylating 2-hydroxy-3,6-dichlorobenzoic acid to form a methylationreaction product comprising 3,6-dichloro-2-methoxybenzoic acid saltand/or ester thereof; and optionally saponifiying the methylationreaction product to form 3,6-dichloro-2-methoxybenzoic acid.
 63. Aprocess for preparing a haloaminoaromatic compound, the processcomprising: feeding hydrogen and a feed mixture comprising ahalonitroaromatic compound to a hydrogenation zone; and reacting thehalonitroaromatic compound with hydrogen in the presence of ahydrogenation catalyst comprising platinum on a carbon support toproduce a reaction product comprising the haloaminoaromatic compound,wherein the process further comprises one or more of the followingfeatures: (1) the hydrogenation catalyst is a calcined hydrogenationcatalyst; (2) the feed mixture further comprises a solvent comprising anacid; (3) the hydrogenation catalyst is an unmodified hydrogenationcatalyst; (4) the feed mixture is free of dehalogenation suppressors;(5) the reaction product further comprises 2-chloroaniline and3-chloroaniline and the mole ratio of 3-chloroaniline to 2-chloroanilineis no greater than about 6:1, no greater than about 5:1, no greater thanabout 4:1, no greater than about 3:1, no greater than about 2:1, or nogreater than about 1:1; (6) the reaction product further comprises2-chloroaniline and 3-chloroaniline, and the loss of selectivity from2,5-dichloroaniline to 2-chloroaniline and 3-chloroaniline is less thanabout 0.4 mol. %, less than about 0.3 mol. %, or less than about 0.2mol. %; and/or (7) the hydrogenation catalyst comprises platinum metalparticles of a size up to 10 nm in their largest dimension and no morethan about 50% (number basis), no more than about 25% (number basis), nomore than about 20% (number basis), no more than about 15% (numberbasis), or no more than about 10% (number basis) of the platinum metalparticles are less than 2 nm in their largest dimension.